livialima

joined 2 years ago
MODERATOR OF
linuxupskillchallenge
sorted by: new top controversial old
12
Day 3 - Power trip! (programming.dev)
 

INTRO

You may have been logging in as an ordinary user at your server, yet you're probably aware that root is the power user on a Linux system. This administrative or "superuser" account, is all powerful - and a typo in a command could potentially cripple your server. As a sysadmin you're typically working on systems that are both important and remote, so avoiding such mistakes is A Very Good Idea.

In ancient times, sysadmins used to login as root in production systems, but it’s now common Best Practice to discourage or disallow login directly by root and instead to give specified trusted users the permission to run root-only commands via the sudo command.

YOUR TASKS TODAY

  • Change the password of your sudo user
  • Change the hostname
  • Change the timezone

Check out the demo

LOCAL CHANGES VS GLOBAL CHANGES

Global: programs/environments that any user can use, used across the system. A global change affects all users. Local or By user: programs/environments that a particular user runs, not available to other users. A local change affects only one user.

WHO ARE YOU AND WHAT CAN YOU DO?

There are 3 types of users in a Linux system:

  • root - the powerful superuser that can execute any command at any level in the system. They can do all global changes as well as local changes for any user.
  • sudoers - regular users that are allowed to use sudo, i.e., they can execute commands in one or more levels in the system, can do some or all global changes. It's common to have at least one sudoer that has the same powers as root, but the amount of priviledges other sudoers have can vary.
  • regular users - users that can use the system but can only do local changes, i.e., can only deal with their own files/directories and environment variables.

We will get into more detail about users and their permissions on Day 13 and Day 14.

STOP USING ROOT

If you created a VM with one of the big VPS providers, root is already "disabled" and your default user (ubuntu, azureuser, etc) already has sudo powers.

However, if you really, really want to use root, there are ways to do it in AWS, Azure and GCP. But do it at your own risk!

However, if you created a VM locally or with other VPS providers, it is very likely that you have your root user readily available.

Stop using root. If you followed the guides, you should have created a regular user and adding it to a sudoers group, like this:

adduser snori74

usermod -a -G sudo snori74

Adding a regular user to a group with sudo priviledges is the easiest way to do it, as the sudo group is pretty standard in Ubuntu. But this can also be accomplished by modifying the /etc/sudoers using the command visudo.

Login with this new user from now on.

CHANGE PASSWORD

If you're using a password to login (rather than public key), then now is a good time to ensure that this is very strong and unique - i.e. at least 10 alphanumeric characters - because your server is fully exposed to bots that will be continuously attempting to break in. Use the passwd command to change your password. To do this, think of a new, secure password, then simply type passwd, press “Enter” and give your current password when prompted, then the new one you've chosen, confirm it - and then WRITE IT DOWN somewhere. In a production system of course, public keys and/or two factor authentication would be more appropriate.

A NOTE ON "HARDENING"

Your server is protected by the fact that its security updates are up to date, and that you've set Long Strong Unique passwords - or are using public keys. While exposed to the world, and very likely under continuous attack, it should be perfectly secure. Next week we'll look at how we can view those attacks, but for now it's simply important to state that while it's OK to read up on "SSH hardening", things such as changing the default port and fail2ban are unnecessary and unhelpful when we're trying to learn - and you are perfectly safe without them.

THE POWER OF SUDO

  • Use the links in the "Resources" section below to understand how sudo works
  • Use ls -l to check the permissions of /etc/shadow - notice that only root has any access. Can you use cat, less or nano to view it?
  • This file is where the hashed passwords are kept. It is a prime target for intruders - who aim to grab it and use offline password crackers to discover the passwords.
  • Now try with sudo, e.g. sudo cat /etc/shadow
  • Test running the reboot command, and then via sudo (i.e. sudo reboot)

Once you've reconnected back:

  • Use the uptime command to confirm that your server did actually fully restart
  • Test fully “becoming root” by the command sudo -i. This can be handy if you have a series of commands to do "as root". Note the change to your prompt.
  • Type exit or logout to get back to your own normal “support” login.
  • Use less to view the file /var/log/auth.log, where any use of sudo is logged
  • You could "filter" this by typing: grep "sudo" /var/log/auth.log

Normally invoking the sudo command will ask you to re-confirm your identity with your password. However, this can be changed in the sudoers configuration file so it does NOT prompt for a password.

ADMINISTRATIVE TASKS

We will go into detail of the many things you can do to your server, but here are some examples of simple administrative tasks that require sudo.

If you wish to, you can now rename your server. Traditionally you would do this by editing two files, /etc/hostname and /etc/hosts and then rebooting - but the more modern, and recommended, way is to use the hostnamectl command; like this:

sudo hostnamectl set-hostname mylittlecloudbox

No reboot is required but if you want to see the new name in the prompt, just open a new session with bash (or logoff and login again, same effect).

For a cloud server, you might find that the hostname changes after a reboot. To prevent this, edit /etc/cloud/cloud.cfg and change the "preserve_hostname" line to read:

preserve_hostname: true

You might also consider changing the timezone your server uses. By default this is likely to be UTC (i.e. GMT) - which is pretty appropriate for a worldwide fleet of servers. You could also set it to the zone the server is in, or where you and your headquarters are. For a company this is a decision not to be taken lightly, but for now you can simply change as you please!

First check the current setting with:

timedatectl

Then get a a list of available timezones:

timedatectl list-timezones

And finally select one, like this:

sudo timedatectl set-timezone Australia/Sydney

Confirm:

timedatectl

The major practical effects of this are (1) the timing of scheduled tasks, and (2) the timestamping of the logs files kept under /var/log. If you make a change, there will naturally be a "jump" in the dates and time recorded.

WRAP

As a Linux sysadmin you may be working on client or custom systems where you have little control, and many of these will default to doing everything as root. You need to be able to safely work on such systems - where your only protection is to double check before pressing Enter.

On the other hand, for any systems where you have full control, setting up a "normal" account for yourself (and any co-admins) with permission to run sudo is recommended. While this is standard with Ubuntu, it's also easy to configure with other popular server distros such as Debian, CentOS and RHEL.

EXTENSION

What's difference between "sudo -i" and "sudo -s"?

Both sudo -i and sudo -s are commands that allow a user to obtain root privileges on a Unix-based system. However, they have some differences in how they function.

  • sudo -i stands for "sudo interactive" and it launches a new login shell for the root user. This means that it creates a new environment for the root user with the root user's home directory and shell configuration files. This makes it similar to logging in directly as the root user, and any commands executed from this shell will have the privileges of the root user.
  • sudo -s stands for "sudo shell" and it launches a new shell for the root user, but it does not create a new login shell. This means that it does not change the environment or shell configuration files of the current user. Any commands executed from this shell will have the privileges of the root user, but the environment will still be that of the current user.

In summary, sudo -i is more powerful and creates a new shell with the full environment of the root user, while sudo -s is less powerful and only launches a new shell with the root user's privileges but with the same environment as the current user.

RESOURCES

Some rights reserved. Check the license terms here

9
Day 2 - Basic navigation (programming.dev)
 

INTRO

Most computer users outside of the Linux and Unix world don't spend much time at the command-line now, but as a Linux sysadmin this is your default working environment - so you need to be skilled in it.

When you use a graphic desktop such as Windows or Apple's macOS (or even the latest Linux flavors), then increasingly you are presented with simple "places" where your stuff is stored - "Pictures" "Music" etc but if you're even moderately technical then you'll realize that underneath all this is a hierarchical "directory structure" of "folders" (e.g. C:\Users\Steve\Desktop on Windows or /Users/Steve/Desktop on macOS - and on a Desktop Linux system /home/steve/Desktop)

From now on, the course will point you to a range of good online resources for a topic, and then set you a simple set of tasks to achieve. It’s perfectly fine to google for other online resources, refer to any books you have etc - and in fact a fundamental element of the design of this course is to force you to do a bit of your own research. Even the most experienced sysadmins will do an online search to find advice for how to use commands - so the sooner you too get into that habit the better!

YOUR TASKS TODAY

  • Find the documentation for the commands we used so far - demo
  • Navigate between directories, then create, list, move and delete files - demo

RTFM

This is a good time to mention that one of the many advantages of Linux is that it's designed to let you know the system, to let you learn how to use it. The documentation available in form of text manuals, guides and forums is where you will spend most of your time during this journey.

Whereas proprietary systems have some free documentation, you see much more frequently the use of paid customer support to fix issues or find how a particular task can be executed. Although you can also do this with Linux (Canonical, RedHat and SuSE are examples of companies that offer support in the same fashion), this is most likely not the case. And you are here to learn, so...

Which leads us to the famous acronym RTFM. Reading the manual is the first thing you should do when you're learning a command. We will go through the many ways to obtain that information but if at the end of that search you need more insight, you can always ask a well written question in forums and other communities.

Starting with the man command. Each application installed comes with its own page in this manual, so that you can look at the page for pwd to see the full detail on the syntax like this:

man pwd

You might also try:

 man cp
 man mv
 man grep
 man ls
 man man

As you’ll see, these are excellent for the detailed syntax of a command, but many are extremely terse, and for others the amount of detail can be somewhat daunting!

And that's why tldr is such a powerful tool! You can easily install it with sudo apt install tldr or follow this demo.

$ tldr pwd
pwd
Print name of current/working directory.More information: https://www.gnu.org/software/coreutils/pwd.

 - Print the current directory:
   pwd

 - Print the current directory, and resolve all symlinks (i.e. show the "physical" path):
   pwd -P

If you know a keyword or some description of what the command is supposed to do, you can try apropos or man -k like this:

$ apropos "working directory"
git-stash (1)        - Stash the changes in a dirty working directory away
pwd (1)              - print name of current/working directory
pwdx (1)             - report current working directory of a process

$ man -k "working directory"
git-stash (1)        - Stash the changes in a dirty working directory away
pwd (1)              - print name of current/working directory
pwdx (1)             - report current working directory of a process

But you'll soon find out that not every command has a manual that you can read with man. Those commands are contained within the shell itself and we call them builtin commands.

There are some overlaping (i.e. builtin commands that also have a man page) but if man does not work, we use help to display information about them.

$ man export
No manual entry for export

$ help export
export: export [-fn] [name[=value] ...] or export -p
    Set export attribute for shell variables.

    Marks each NAME for automatic export to the environment of subsequently
    executed commands.  If VALUE is supplied, assign VALUE before exporting.

    Options:
      -f        refer to shell functions
      -n        remove the export property from each NAME
      -p        display a list of all exported variables and functions

    An argument of `--' disables further option processing.

    Exit Status:
    Returns success unless an invalid option is given or NAME is invalid.

The best way to know if a command is a builtin command, is to check its type:

$ type export
export is a shell builtin

And lastly, info reads the documentation stored in info format.

NAVIGATE THE FILE STRUCTURE

  • Start by reading the manual: man hier
  • / is the "root" of a branching tree of folders (also known as directories)
  • At all times you are "in" one part of the system - the command pwd ("print working directory") will show you where you are
  • Generally your prompt is also configured to give you at least some of this information, so if I'm "in" the /etc directory then the prompt might be steve@202.203.203.22:/etc$ or simply /etc: $
  • cd moves to different areas - so cd /var/log will take you into the /var/log folder - do this and then check with pwd - and look to see if your prompt changes to reflect your location.
  • You can move "up" the structure by typing cd .. ( "cee dee dot dot ") try this out by first cd'ing to /var/log/ then cd .. and then cd .. again - watching your prompt carefully, or typing pwd each time, to clarify your present working directory.
  • A "relative" location is based on your present working directory - e.g. if you first cd /var then pwd will confirm that you are "in" /var, and you can move to /var/log in two ways - either by providing the full path with cd /var/log or simply the "relative" path with the command cd log
  • A simple cd will always return you to your own defined "home directory", also referred to as ~ (the "tilde" character) [NB: this differs from DOS/Windows]
  • What files are in a folder? The ls (list) command will give you a list of the files, and sub folders. Like many Linux commands, there are options (known as "switches") to alter the meaning of the command or the output format. Try a simple ls, then ls -l -t and then try ls -l -t -r -a
  • By convention, files with a starting character of "." are considered hidden and the ls, and many other commands, will ignore them. The -a switch includes them. You should see a number of hidden files in your home directory.
  • A note on switches: Generally most Linux command will accept one or more "parameters", and one or more "switches". So, when we say ls -l /var/log the "-l" is a switch to say "long format" and the "/var/log" is the "parameter". Many commands accept a large number of switches, and these can generally be combined (so from now on, use ls -ltra, rather than ls -l -t -r -a
  • In your home directory type ls -ltra and look at the far left hand column - those entries with a "d" as the first character on the line are directories (folders) rather than files. They may also be shown in a different color or font - if not, then adding the "--color=auto" switch should do this (i.e. ls -ltra --color=auto)

BASIC DIRECTORY MANIPULATION

  • You can make a new folder/directory with the mkdir command, so move to your home directory, type pwd to check that you are indeed in the correct place, and then create a directory, for example to create one called "test", simply type mkdir test. Now use the ls command to see the result.
  • You can create even more directories, nesting inside directories, and then navigate between them with the cd command.
  • When you want to move that directory inside another directory, you use mv and specify the path to move.
  • To delete (or remove) a directory, use rmdir if the directory is empty or rm -r if there still any files or other directories inside of it.

BASIC FILE MANIPULATION

  • You can make new empty files with the touch command, so you can explore a little more of the ls command.
  • When you want to move that file to another directory, you use mv and specify the path to move.
  • To delete (or remove) a file, use rm.

WRAP

Being able to move confidently around the directory structure at the command line is important, so don’t think you can skip it! However, these skills are something that you’ll be constantly using over the twenty days of the course, so don’t despair if this doesn’t immediately “click”.

EXTENSION

If this is already something that you’re very familiar with, then:

  • Learn about pushd and popd to navigate around multiple directories easily. Running pushd /var/log moves you to to the /var/log, but keeps track of where you were. You can pushd more than one directory at a time. Try it out: pushd /var/log, pushd /dev, pushd /etc, pushd, popd, popd. Note how pushd with no arguments switches between the last two pushed directories but more complex navigation is also possible. Finally, cd - also moves you the last visited directory.

RESOURCES

Some rights reserved. Check the license terms here

7
Day 1 - Get to know your server (programming.dev)
 

INTRO

You should now have a remote server setup running the latest Ubuntu Server LTS (Long Term Support) version. You alone will be administering it. To become a fully-rounded Linux server admin you should become comfortable working with different versions of Linux, but for now Ubuntu is a good choice.

Once you have reached a level of comfort at the command-line then you'll find your skills transfer not only to all the standard Linux variants, but also to Android, Apple's OSX, OpenBSD, Solaris and IBM AIX. Throughout the course you'll be working on Linux - but in fact most of what is covered is applicable to any system derived from the UNIX Operating System - and the major differences between them are with their graphic user interfaces such as Gnome, Unity, KDE etc - none of which you’ll be using!

YOUR TASKS TODAY

  • Connect and login to your server, preferably using a SSH client
  • Run a few simple commands to check the status of your server - like this demo

USING A SSH CLIENT

Remote access used to be done by the simple telnet protocol, but now the much more secure SSH (Secure SHell) protocol is always used. If your server is a local VM or WSL, you could skip this section by simply using the server console/terminal if you want. We will explore SSH more in detail at the server side on Day 3 but knowing how to use a ssh client is a basic sysadmin skill, so you might as well do it now.

In MacOS and Linux

On an MacOS machine you'll normally access the command line via Terminal.app - it's in the Utilities sub-folder of Applications.

On Linux distributions with a menu you'll typically find the terminal under "Applications menu -> Accessories -> Terminal", "Applications menu -> System -> Terminal" or "Menu -> System -> Terminal Program (Konsole)"- or you can simply search for your terminal application. In many cases Ctrl+Alt+T will also bring up a terminal windows.

Once you open up a "terminal" session, you can use your command-line ssh client like this:

ssh user@

For example:

ssh support@192.123.321.99

If the remote server was configured with a SSH public key (like AWS, Azure and GCP), then you'll need to point to the location of the private key as proof of identity with the -i switch, typically like this:

ssh -i ~/.ssh/id_rsa support@192.123.321.99

A very slick connection process can be setup with the .ssh/config feature - see the "SSH client configuration" link in the EXTENSION section below.

In Windows

On recent Windows 10 versions, the same command-line client is now available, but must be enabled (via "Settings", "Apps", "Apps & features", "Manage optional features", "Add a feature", "OpenSSH client").

There are various SSH clients available for Windows (PuTTY, Solar-PuTTY, MobaXterm, Termius, etc) but if you use Windows versions older than 10, the installation of PuTTY is suggested.

Alternatively, you can install the Windows Subsystem for Linux which gives you a full local command-line Linux environment, including an SSH client - ssh.

Regardless of which client you use, the first time you connect to your server, you may receive a warning that you're connecting to a new server - and be asked if you wish to cache the host key. Yes, you do. Just type/click Yes.

But don't worry too much about securing the SSH session or hardening the server right now; we will be doing this in Day 3.

For now, just login to your server and remember that Linux is case-sensitive regarding user names, as well as passwords.

You'll be spending a lot of time in your SSH client, so it pays to spend some time customizing it. At the very least try "black on white" and "green on black" - and experiment with different monospaced fonts, ("Ubuntu Mono" is free to download, and very nice).

It's also very handy to be able to cut and paste text between your remote session and your local desktop, so spend some time getting confident with how to do this in your SSH client and terminal.

Perhaps you might now try logging in from home and work - even from your smartphone! - using an ssh client app such as Termux, Termius for Android or Termius for iPhone. As a server admin you'll need to be comfortable logging in from all over. You can also potentially use JavaScript ssh clients like consolefish and ShellHub, but these options involve putting more trust in third-parties than most sysadmins would be comfortable with when accessing production systems.

To log out, simply type exit or close the terminal.

LOGIN TO YOUR SERVER

Once logged in, notice that the "command prompt" that you receive ends in $ - this is the convention for an ordinary user, whereas the "root" user with full administrative power has a # prompt (but we will dive into this difference in Day 3 as well).

Here's a short vid on using ssh in a work environment.

GENERAL INFORMATION ABOUT THE SERVER

Use lsb_release -a to see which Linux distro and version you're using. lsb_release may not be available in your server, as it's not widely adopted, but you will always have the same information available in the system file os-release. You can check its content by typing cat /etc/os-release

uname -a will also print the system information and it can show some interesting things like kernel version, hardware platform, etc.

uptime will show you how long the system has been running. It kinda makes the weird numbers you get from cat /proc/uptime a lot more readable.

whoami will print the user name you logged on with, who will show who is logged on and w will also show what they are doing.

HARDWARE INFORMATION

lshw can give some detailed information on the hardware configuration, and there's a bunch of switches we can use to filter the information we want to see, but it's not the only tool we use to check hardware with. Some of the used commands are:

MEASURE MEMORY AND CPU USAGE

Don't worry! Linux won't eat your RAM. But if you want to check the amount of memory used in the system, use free -h . vmstat will also give some memory statistics.

top is like a Task Manager for Linux, it will display the processes and the consumption of resources. htop is an interactive, prettier version.

MEASURE DISK USAGE

Use df -h to see disk space usage, but go with du -h if you want to estimate the size of your folders.

MEASURE NETWORK USAGE

You will have a general idea of your network interfaces and their IP addresses by using ifconfig or its modern substitute ip address, but it won't show you bandwidth usage.

For that we have netstat -i in a more static view and ifstat in a continuous view. To interrupt ifstat just use CTRL+C.

But if you want more info on that traffic, sudo iftop -i eth0 is a nice display. Change eth0 for the interface you wish to capture traffic information. To exit the monitor view, type q to quit.

POSTING YOUR PROGRESS

Regularly posting your progress can be a helpful motivator. Feel free to post to the subreddit/community or to the discord chat a small introduction of yourself, and your Linux background for your "classmates" - and notes on how each day has gone.

Of course, also drop in a note if you get stuck or spot errors in these notes.

EXTENSION

If this was all too easy, then spend some time reading up on:

RESOURCES

Some rights reserved. Check the license terms here

5
Day 0 - Creating Your Own Local Server (programming.dev)
submitted 2 years ago* (last edited 2 years ago) by livialima@programming.dev to c/linuxupskillchallenge@programming.dev
0 comments fedilink
 

It's difficult to create a server in cloud without a credit card

We normally recommend using Amazon's AWS "Free Tier" or Digital Ocean - but both require that you have a credit card. The same is true of the Microsoft Azure, Google's GCP and the vast majority of providers listed at Low End Box ().

Some will accept PayPal, or Bitcoin - but typically those who don't have a credit card don't have these either.

WARNING: If you go searching too deeply for options in this area, you're very likely to come across a range of scammy, fake, or fraudulent sites. While we've tried to eliminate these from the links below, please do be careful! It should go without saying that none of these are "affiliate" links, and we get no kick-backs from any of them :-)

Cards that work as, or like, credit cards

But what if I don’t want to use a cloud provider? You can just work with a local virtual machine

You can run the challenge on a home server and all the commands will work as they would on a cloud server. However, not being exposed to the wild certainly loses the feel of what real sysadmins have to face.

If you set your own VM at a private server, go for the minimum requirements like 1GHz CPU core, 1GB RAM, and a couple of gigs of disk space. You can always adapt this to your heart's desire (or how much hardware you have available).

Our recommendation is: use a cloud server if you can, to get the full experience, but don't get limited by it. This is your server.

Download the Linux ISO

Go to the Official Ubuntu page and download the latest LTS (Long Term Support) available version.

NOTE: download the server version, NOT the desktop version.

Create a Virtual Machine with VirtualBox

Install VirtualBox, when ready:

  • Click on Machine > New
  • Give a name to your VM and select the Type Linux. Click Next.
  • Adjust hardware: 1024MB memory and 1 CPU (this is the minimum, but you can reserve more if your host machine can provide it). Click Next
  • Virtual hard disk: 2,5GB is minimum, 5GB is a good number. Click Next.
  • Finish but we're not done yet.
  • The new VM should show up in a list of VMs, select it.
  • Click on Machine > Settings
  • Click on Storage. Right-click on Controllet IDE, click on Optical Drive.
  • Select the Linux ISO you downloaded from the list if available, if not click Add and find it in your directories. Click Choose.
  • Click on Network and change the network adapter to Bridged Adapter.
  • Click OK
  • Click Start or Machine > Start > Normal Start.

Installing Linux

After a few seconds the welcome screen will load. At the end of each page there's DONE and BACK buttons. Use arrow keys and the enter key to select options. When you're ok with your selection, use the arrow key to go down to DONE and enter to go to the next page.

  • Welcome Screen: Select your language
  • Keyboard Configuration: Select Keyboard type
  • Choose type of install: Select Ubuntu Server (minimized). It comes with most of the packages you need without being bloated. It will install faster too.
  • Network Connections: If you have setup the VM to use a bridged adapter like instructed, you don’t really have to worry a lot. The installer will automatically detect the DHCP settings from your local network router and you just have to select DONE.
  • Configure Proxy: If your system requires any http proxy to connect to the internet enter the proxy address, otherwise just select DONE.
  • Configure Ubuntu archive mirror: Leave it as default. DONE.
  • Guided Storage Configurations: We are going to utilize the entire storage space reserved for this VM and that's why we select Use the Entire Disk option.
  • Storage Configuration: Leave it the standard storage configuration and select DONE. When prompted to confirm, don't worry. This will only use the VM disk, not your computer disk.
  • Profile Setup: Enter your name, your server’s name, your username and password. This user will be your administrator user in the system (or sudo), so don't forget this password.
  • Update to Ubuntu Pro: No. Skip for now.
  • SSH setup: Select on Install OpenSSH server because that’s how you will connect to your server later.
  • Featured Server Snaps: None of these packages are important now, just select DONE.
  • Installing System: Now you have to wait for a few minutes for your system to install. You can "cheat" and speed up the install by skipping the downloading of updates, select Cancel update and Reboot when it appears at the bottom of the page, a few moments later. You can complete the updates after the first boot. After the installation is complete the system will reboot automatically.

Logging in for the first time

After the first reboot, it will show a black screen asking for the login. That's when you use that username and password you created during the install.

Note: the password will not show up, not even ***, just trust that is taking it in.

If you need to find out the IP address for the VM, just type in the console:

ip address

That will give you the inet, i.e., the ip address. You will need that to connect with SSH.

Remote access via SSH

If you are using Windows 10 or 11, follow the instructions to connect using the native SSH client. In older versions of Windows, you may need to install a 3rd party SSH client, like PuTTY and generate a ssh key-pair.

If you are on Linux or MacOS, open a terminal and run the command:

ssh username@ip_address

Or, using the SSH private key, ssh -i private_key username@ip_address

Enter your password (or a passphrase, if your SSH key is protected with one)

Voila! You have just accessed your server remotely.

If in doubt, consult the complementary video that covers a lot of possible setups (local server with VirtualBox, AWS, Digital Ocean, Azure, Linode, Google Cloud, Vultr and Oracle Cloud).

You are now a sysadmin

Confirm that you can do administrative tasks by typing:

sudo apt update

Then:

sudo apt upgrade -y

Don't worry too much about the output and messages from these commands, but it should be clear whether they succeeded or not. (Reply to any prompts by taking the default option). These commands are how you force the installation of updates on an Ubuntu Linux system, and only an administrator can do them.

REBOOT

When a kernel update is identified in this first check for updates, this is one of the few occasions you will need to reboot your server, so go for it after the update is done:

sudo reboot now

Your server is now all set up and ready for the course!

Note that:

  • This server is now running but is not exposed to the Internet, i.e. other people will not be able to attempt to connect. We recommend you keep it that way. It is one thing to expose a server in the cloud, exposing your home network is another story. For your own security, don't do it.

To logout, type logout or exit.

When you are done

Just type:

sudo shutdown now

Or click on Force Shutdown

Some Other Options

Now you are ready to start the challenge. Day 1, here we go!

16
Day 0 - Creating Your Own Server in the Cloud (but cheaper) (programming.dev)
 

INTRO

First, you need a server. You can't really learn about administering a remote Linux server without having one of your own - so today we're going to buy one!

Through the magic of Linux and virtualization, it's now possible to get a small Internet server setup almost instantly - and at very low cost. Technically, what you'll be doing is creating and renting a VPS ("Virtual Private Server"). In a datacentre somewhere, a single physical server running Linux will be split into a dozen or more Virtual servers, using the KVM (Kernel-based Virtual Machine) feature that's been part of Linux since early 2007.

In addition to a hosting provider, we also need to choose which "flavour" of Linux to install on our server. If you're new to Linux then the range of "distributions" available can be confusing - but the latest LTS ("Long Term Support") version of Ubuntu Server is a popular choice, and what you'll need for this course.

Signing up with a VPS

Sign-up is immediate - just provide your email address and a password of your choosing and you're in! To be able to create a VM, however, you may need to provide your credit card information (or other information for billing) in the account section.

Comparison

Provider Instance Type vCPU Memory Storage Price Trial Credits
Digital Ocean Basic Plan 1 1 GB 25 GB SSD $6.00 $200 / 60 days
Linode Nanode 1GB 1 1 GB 25 GB SSD $5.00 $100 / 60 days
Vultr Cloud Compute - Regular 1 1 GB 25 GB SSD $5.00 $250 / 30 days

For more details:

Create a Virtual Machine

The process is basically the same for all these VPS, but here some step-by-steps:

VM with Digital Ocean (or Droplet)

  • Choose "Manage, Droplets" from the left-hand sidebar. (a "droplet" is Digital Ocean's cute name for a server!)
  • Click on Create > Droplet
  • Choose Region: choose the one closes to you. Be aware that the pricing can change depending on the region.
  • DataCenter: use the default (it will pick one for you)
  • Choose an image: Select the image "Ubuntu" and opt for the latest LTS version
  • Choose Size: Basic Plan (shared CPU) + Regular. Click the option with 1GB Mem / 1 CPU / 25GB SSD Disk
  • Choose Authentication Method: choose "Password" and type a strong password for the root account.
  • Note that since the server is on the Internet it will be under immediate attack from bots attempting to "brute force" the root password. Make it strong!
  • Or, if you want to be safer, choose "SSH Key" and add a new public key that you created locally
  • Choose a hostname because the default ones are pretty ugly.
  • Create Droplet

VM with Linode (or Node)

  • Click on Create Linode (a "linode" is Linode's cute name for a server)
  • Choose an Distribution: Select the image "Ubuntu" and opt for the latest LTS version
  • Choose Region: choose the one closest to you. Be aware that the pricing can change depending on the region.
  • Linode Plan: Shared CPU + Nanode 1GB. This option has 1GB Mem / 1 CPU / 25GB SSD Disk
  • Linode Label: Choose a hostname because the default ones are pretty ugly.
  • Choose Authentication Method: on the "Root Password" and type a strong password for the root account.
  • Note that since the server is on the Internet it will be under immediate attack from bots attempting to "brute force" the root password. Make it strong!
  • And, if you want to be safer, click "Add An SSH Key" and add a new public key that you created locally
  • Create Linode

VM with Vultr

  • Choose "Products, Instances" from the left-hand sidebar. (no cute names)
  • Click on Deploy Server
  • Choose Server: Cloud Compute (Shared vCPU) + Intel Regular Performance
  • Server Location: choose the one closest to you. Be aware that the pricing can change depending on the region.
  • Server image: Select the image "Ubuntu" and opt for the latest LTS version
  • Server Size: Click the option with 1GB Mem / 1 CPU / 25GB SSD Disk
  • SSH Keys: click "Add New" and add a new public key that you created locally
  • Note that since that there's no option to just authenticate with root password, you will need to create a SSH key.
  • Server Hostname & Label: Choose a hostname for your server.
  • Disable "Auto Backups". They will not be required for the challenge and are only adding to the bill.
  • Deploy Now

Logging in for the first time with console

We are going to access our server using SSH but, if for some reason you get stuck in that part, there is a way to access it using a console:

Remote access via SSH

You should see a "Public IPv4 address" (or similar) entry for your server in account's control panel, this is its unique Internet IP address, and it is how you'll connect to it via SSH (the Secure Shell protocol) - something we'll be covering in the first lesson.

  • Digital Ocean: Click on Networking tab > Public Network > Public IPv4 Address
  • Linode: Click on Network tab > IP Addresses > IPv4 - Public
  • Vultr: Click on Settings tab > Public Network > Address

If you are using Windows 10 or 11, follow the instructions to connect using the native SSH client. In older versions of Windows, you may need to install a 3rd party SSH client, like PuTTY and generate a ssh key-pair.

If you are on Linux or MacOS, open a terminal and run the command:

ssh username@ip_address

Or, using the SSH private key, ssh -i private_key username@ip_address

Enter your password (or a passphrase, if your SSH key is protected with one)

Voila! You have just accessed your server remotely.

If in doubt, consult the complementary video that covers a lot of possible setups (local server with VirtualBox, AWS, Digital Ocean, Azure, Linode, Google Cloud, Vultr and Oracle Cloud).

Creating a working admin account

We want to follow the Best Practice of not logging as "root" remotely, so we'll create an ordinary user account, but one with the power to "become root" as necessary, like this:

adduser snori74

usermod -a -G admin snori74

usermod -a -G sudo snori74

(Of course, replace 'snori74' with your name!)

This will be the account that you use to login and work with your server. It has been added to the 'adm' and 'sudo' groups, which on an Ubuntu system gives it access to read various logs and to "become root" as required via the sudo command.

To login using your new user, copy the SSH key from root.

You are now a sysadmin

Confirm that you can do administrative tasks by typing:

sudo apt update

Then:

sudo apt upgrade -y

Don't worry too much about the output and messages from these commands, but it should be clear whether they succeeded or not. (Reply to any prompts by taking the default option). These commands are how you force the installation of updates on an Ubuntu Linux system, and only an administrator can do them.

REBOOT

When a kernel update is identified in this first check for updates, this is one of the few occasions you will need to reboot your server, so go for it after the update is done:

sudo reboot now

Your server is now all set up and ready for the course!

Note that:

  • This server is now running, and completely exposed to the whole of the Internet
  • You alone are responsible for managing it
  • You have just installed the latest updates, so it should be secure for now

To logout, type logout or exit.

When you are done

You should be safe running the VM during the month for the challenge, but you can Stop the instance at any point. It will continue to count to the bill, though.

When you no longer need the VM, Terminate/Destroy instance.

Now you are ready to start the challenge. Day 1, here we go!

5
Day 0 - Creating Your Own Server in the Cloud (programming.dev)
 

INTRO

First, you need a server. You can't really learn about administering a remote Linux server without having one of your own - so today we're going get one - completely free!

Through the magic of Linux and virtualisation, it's now possible to get a small Internet server setup almost instantly - and at very low cost. Technically, what you'll be doing is creating and renting a VPS ("Virtual Private Server"). In a datacentre somewhere, a single physical server running Linux will be split into a dozen or more Virtual servers, using the KVM (Kernel-based Virtual Machine) feature that's been part of Linux since early 2007.

In addition to a hosting provider, we also need to choose which "flavour" of Linux to install on our server. If you're new to Linux then the range of "distributions" available can be confusing - but the latest LTS ("Long Term Support") version of Ubuntu Server is a popular choice, and what you'll need for this course.

Signing up with a VPS

Sign-up is fairly simple - just provide your email address and a password of your choosing - along with a phone number for a 2FA or another second method of authentication. You will need to also provide your credit card information.

Comparison

Provider Instance Type vCPU Memory Storage Price* Trial Credits
AWS t2.micro 1 1 GB 8 GB SSD $18.27 Free Tier for 1 year
Azure B1 1 1 GB 30 GB SSD $12.26 $200 / 30 days + Free Tier for 1 year
GCP e2-micro 1 1 GB 10 GB SSD $ 7.11 $300 / 90 days
Oracle VM.Standard.E2.1.Micro 1 1 GB 45 GB SSD $19.92 $300 / 30 days + Always Free services
  • Estimate prices

On a side note, avoid IBM Cloud as much as you can. They do not offer good deals and, according to some reports from previous students, their Linux VM is tampered enough to the point some commands do not work as expected.

Educational Packs

Create a Virtual Machine

The process is basically the same for all these VPS, but here some step-by-steps:

VM with Oracle Cloud

  • Choose "Compute, Instances" from the left-hand sidebar menu.
  • Click on Create Instance
  • Choose a hostname because the default ones are pretty ugly.
  • Placementn: it will automatically choose the one closes to you.
  • Change Image: Select the image "Ubuntu" and opt for the latest LTS version
  • Change Shape: Click on "Specialty and previous generation". Click VM.Standard.E2.1.Micro - the option with 1GB Mem / 1 CPU / Always Free-eligible
  • Add SSH Keys: select "Generate a key pair for me" and download the private key to connect with SSH. You can also add a new public key that you created locally
  • Create

Logging in for the first time

Select your instance and click "ssh" it will open a new window console. To access the root, type "sudo -i passwd" in the command line then set your own password. Log in by typing "su" and "password". Note that the password won't show as you type or paste it.

Remote access via SSH

You should see a "Public IPv4 address" (or similar) entry for your server in account's control panel, this is its unique Internet IP address, and it is how you'll connect to it via SSH (the Secure Shell protocol) - something we'll be covering in the first lesson.

If you are using Windows 10 or 11, follow the instructions to connect using the native SSH client. In older versions of Windows, you may need to install a 3rd party SSH client, like PuTTY and generate a ssh key-pair.

If you are on Linux or MacOS, open a terminal and run the command:

ssh username@ip_address

Or, using the SSH private key, ssh -i private_key username@ip_address

Enter your password (or a passphrase, if your SSH key is protected with one)

Voila! You have just accessed your server remotely.

If in doubt, consult the complementary video that covers a lot of possible setups (local server with VirtualBox, AWS, Digital Ocean, Azure, Linode, Google Cloud, Vultr and Oracle Cloud).

What about the root user?

Working on a different approach from smaller VPS, the big guys don't let use root to connect. Don't worry, root still exists in the system, but since the provider already created an admin user from the beginning, you don't have to deal with it.

You are now a sysadmin

Confirm that you can do administrative tasks by typing:

sudo apt update

(Normally you'd expect this would prompt you to confirm your password, but because you're using public key authentication the system hasn't prompted you to set up a password - and AWS have configured sudo to not request one for "ubuntu").

Then:

sudo apt upgrade -y

Don't worry too much about the output and messages from these commands, but it should be clear whether they succeeded or not. (Reply to any prompts by taking the default option). These commands are how you force the installation of updates on an Ubuntu Linux system, and only an administrator can do them.

REBOOT

When a kernel update is identified in this first check for updates, this is one of the few occasions you will need to reboot your server, so go for it:

sudo reboot now

Your server is now all set up and ready for the course!

Note that:

  • This server is now running, and completely exposed to the whole of the Internet
  • You alone are responsible for managing it
  • You have just installed the latest updates, so it should be secure for now

To logout, type logout or exit.

When you are done

You should be safe running the VM during the month for the challenge, but you can Stop the instance at any point. It will continue to count to the bill, though.

When you no longer need the VM, Terminate/Destroy instance.

Now you are ready to start the challenge. Day 1, here we go!

8
PLEASE READ THIS FIRST! HOW THIS WORKS & FAQ (programming.dev)
 

RESOURCES

HOW THIS WORKS

In a nutshell

  • Completely free and open source
  • Focused on practical skills
  • Heavily hands-on
  • Starts at the 1st Monday of each month
  • Runs for 20 weekdays (Mon-Fri)
  • Often points to curated external links, expanding on the topic of the day.
  • Much less ‘formal’ than RHEL or Linux Foundation training

Requirements

  • A cloud-based Ubuntu Linux server - full instructions on how to set this up are in the ‘Day 0’ lessons
  • Basic computer literacy - no prior knowledge of Linux is required but you should be fairly confortable operating your own Windows/Mac machine
  • Requires a daily commitment of 1-2 hours each day for a month but can be self-paced

FREQUENTLY ASKED QUESTIONS - FAQ

Is this course for me?

This course is primarily aimed at two groups:

  1. Linux users who aspire to get Linux-related jobs in industry, such as junior Linux sysadmin, devops-related work and similar, and
  2. Windows server admins who want to expand their knowledge to be able to work with Linux servers.

However, many others have happily used the course simply to improve their Linux command line skills or to learn Linux for the first time – and that’s just fine too.

Will I pass LPIC/RHCA/LFCS/Linux+ certification if I take this course?

NO! This is NOT a preparation course for any Linux certification exam. It can help you, sure, but please refer to a more specific cert training if that's what you are aiming for.

When does it start?

The course always starts on the first Monday of the month. One of the key elements of the course is that the material is delivered in 20 bite-sized lessons, one each workday.

How long does it take? How many hours should I dedicate to it?

Depending on your experience and dedication, you can expect to spend 1-2 hours going through each lesson. The first few days are pretty basic and it might take you just minutes, but there's generally some "Extension" items to spice things up a bit.

I just learned about the challenge and it's already on Day X. Should I wait for next month to start?

Only if you want to. The material is available year-round so you can totally self-pace this if you prefer.

Do I really need a cloud-based server?

Yes, if you’re in the target audience (see above) you definitely should. The fact that such a server is very remote, and open to attack from the whole Internet, “makes it real”. Learning how to setup such a VPS is also a handy skill for any sysadmin.

Instructions for setting up a suitable server with a couple of providers are in the "Day 0" lessons. By all means use a different provider, but ensure you use Ubuntu LTS (preferably the latest version) and either use public key authentication or a Long, Strong, Unique password (we also have instructions on how to do that).

Of course, you’re perfectly entitled to use a local VM, a Raspberry Pi or even just WSL instead – and all of these will work fine for the course material. Just keep in mind what you are missing.

But what if I don't have a credit card (or don't want to use one) to setup an AWS/Azure/GCP server?

Please read Day 0 - Creating Your Own Local Server. There are other options of cloud providers and different payment options. But if none of them works for you, try creating your own local VM.

But what if I don’t want to use a cloud provider? I have a server/VM at home.

Then use your server. Check the post Day 0 - Creating Your Own Local Server

Why Ubuntu, can I use another distro?

The notes assume Ubuntu Server LTS (latest version) and it would be messy to include instructions/variations for other distros (at least right now). If you use Debian or other Debian-based distros (Mint, Pop!OS, Kali) it will make little to no difference because they all have the same structure.

But if you choose RedHat-based distros (Fedora, CentOS, AlmaLinux) or distros like Arch, Gentoo, OpenSUSE, you yourself will need to understand and cope with any differences (e.g. apt vs yum vs pacman).

If none of those names make any sense to you, you shouldn't be picking distros. Go read Linux Journey first lesson instead.

Should I be stopping or terminating my server when not in use?

Using a free-tier VPS, the load of the course does not exceed any thresholds. You can leave it running during the challenge but it's good to keep an eye on it (i.e. don't forget about it later or your provider will start charging you).

I noticed there was a kernel update, but no one said to reboot.

Reboot it. This is one of the few occasions you will need to reboot your server, go for it. The command for that is sudo reboot now

I still have questions/doubts! What do I do?!

Feel free to post questions or comments in Lemmy, Reddit or chat using the Discord server.

If you are inclined to contribute to the material and had the means to do it (i.e. a github account) you can submit an issue to the source directly.

CREDITS

The magnificent Steve Brorens is the mastermind behind the Linux Upskill Challenge. Unfortunately, he passed away but not before ensuring the course would continue to run in his absence. We miss you, snori.

Livia Lima is the one currently maintaining the material. Give her a shout out on Mastodon or LinkedIn.

17
Spread the word! Next course starts on Monday, 6 November 2023 (programming.dev)
 

Just a reminder that the course always restarts on the first Monday of the next month.

Apologies for not posting during October, I'm still setting up the bot to post things automatically.

Don't forget to spread the word and bring your friends!

10
Day 21 - What next? (programming.dev)
 

What is this madness – surely the course was for just 20 days?

Yes, but hopefully you’ll go on learning, so here’s a few suggestions for directions that you might take

Play with your server

You’re familiar with the server you used during the course, so keep working with it. Maybe uninstall Apache2 and install NGINX, a competing webserver. Keep a running stat on ssh “attackers”. Whatever. A free AWS will last a year, and a $5/mo server should be something you can easily justify.

Add services that you’ll use

You should now be capable of following tutorials on installing and running your own instance of Minecraft, Wordpress, WireGuard VPN, or Mediawiki. Expect to have some problems – it's all good experience!

Extend your learning

Stop browsing articles on Gnome, KDE or i3 – and start checking out any articles like “20 Linux commands every sysadmin should know”. Try these out, delve into the options. Like learning a foreign vocabulary, you will only be able to use these “words” if you know them!

Certs

If you’re looking to do Linux professionally, and you don’t have an impressive CV or resume already, then you should be aiming at getting a cert. There are really just three certs/tracks that count:

Even if you don’t want/need certs, the outline of the topics in these references can give you a good idea of areas to focus on in your self-learning.

Affordable professional training

Show your appreciation!

Steve (@snori74) was a collector of postcards and enjoyed greatly all the "Snail Mail" he received from the students.

But since his passing there's nowhere to send postcards anymore. You can show your appreciation for the course by letting everyone else know how awesome it was! Show the world you finished the challenge by posting about it on social media.

Thanks for all and happy linuxing!

14
Day 20 - Scripting (programming.dev)
 

INTRO

Today is the final session for the course. Pat yourself on the back if you worked your way through all lessons!

You’ve seen that a continual emphasis for a sysadmin is to automate as much as possible, and also how in Linux the system is very “transparent” - once you know where to look!

Today, on this final session for the course, we’ll cover how to write small programs or “shell scripts” to help manage your system.

When typing at the Linux command-line you're directly communicating with "the command interpreter", also known as "the shell". Normally this shell is bash, so when you string commands together to make a script the result can be called either a '"shell script", or a "bash script".

Why make a script rather than just typing commands in manually?

  • It saves typing. Remember when we searched through the logs with a long string of grep, cut and sort commands? If you need to do something like that more than a few times then turning it into a script saves typing - and typos!
  • Parameters. One script can be used to do several things depending on what parameters you provide
  • Automation. Pop your script in /etc/cron.daily and it will run each day, or install a symlink to it in the appropriate /etc/rc.d folder and you can have it run each time the system is shut down or booted up.

START WITH A SHEBANG!

Scripts are just simple text files, but if you set the "execute" permissions on them then the system will look for a special line starting with the two characters “#” and “!” - referred to as the "shebang" (or "crunchbang") at the top of the file.

This line typically looks like this:

 #!/bin/bash

Normally anything starting with a "#" character would be treated as a comment, but in the first line and followed by a "!", it's interpreted as: "please feed the rest of this to the /bin/bash program, which will interpret it as a script". All of our scripts will be written in the bash language - the same as you’ve been typing at the command line throughout this course - but scripts can also be written in many other "scripting languages", so a script in the Perl language might start with #!/usr/bin/perl and one in Python #!/usr/bin/env python3

YOUR FIRST SCRIPT

You'll write a small script to list out who's been most recently unsuccessfully trying to login to your server, using the entries in /var/log/auth.log.

Use vim to create a file, attacker, in your home directory with this content:

 #!/bin/bash
 #
 #   attacker - prints out the last failed login attempt
 #
 echo "The last failed login attempt came from IP address:"
 grep -i "disconnected from" /var/log/auth.log|tail -1| cut -d: -f4| cut -f7 -d" "

Putting comments at the top of the script like this isn't strictly necessary (the computer ignores them), but it's a good professional habit to get into.

To make it executable type:

chmod +x attacker

Now to run this script, you just need to refer to it by name - but the current directory is (deliberately) not in your $PATH, so you need to do this either of two ways:

 /home/support/attacker
 ./attacker

Once you're happy with a script, and want to have it easily available, you'll probably want to move it somewhere on your $PATH - and /usr/local/bin is a normally the appropriate place, so try this:

sudo mv attacker /usr/local/bin/attacker

...and now it will Just Work whenever you type attacker

EXTENDING THE SCRIPT

You can expand this script so that it requires a parameter and prints out some syntax help when you don't give one. There are a few new tricks in this, so it's worth studying:

 #
 ##   topattack - list the most persistent attackers
 #
 if [ -z "$1" ]; then
 echo -e "\nUsage: `basename $0`  - Lists the top  attackers by IP"
 exit 0
 fi
 echo " "
 echo "Persistant recent attackers"
 echo " "
 echo "Attempts      IP "
 echo "-----------------------"
 grep "Disconnected from authenticating user root" /var/log/auth.log|cut -d: -f 4 | cut -d" " -f7|sort |uniq -c |sort -nr |head -$1

Again, use vim to create "topattack", chmod to make it executable and mv to move it into /usr/local/bin once you have it working correctly.

(BTW, you can use whois to find details on any of these IPs - just be aware that the system that is "attacking" you may be an innocent party that's been hacked into).

A collection of simple scripts like this is something that you can easily create to make your sysadmin tasks simpler, quicker and less error prone.

If automating and scripting many of your daily tasks sounds like something you really like doing, you might also want to script the setup of your machines and services. Even though you can do this using bash scripting like shown in this lesson, there are some benefits in choosing an orchestration framework like ansible, cloudinit or terraform. Those frameworks are outside of the scope of this course, but might be worth reading about.

And yes, this is the last lesson - so please, feel free to write a review on how the course went for you and what you plan to do with your new knowledge and skills!

RESOURCES

Some rights reserved. Check the license terms here

12
Day 19 - Inodes, symlinks and other shortcuts (programming.dev)
 

INTRO

Today's topic gives a peek “under the covers” at the technical detail of how files are stored.

Linux supports a large number of different “filesystems” - although on a server you’ll typically be dealing with just ext3 or ext4 and perhaps btrfs - but today we’ll not be dealing with any of these; instead with the layer of Linux that sits above all of these - the Linux Virtual Filesystem.

The VFS is a key part of Linux, and an overview of it and some of the surrounding concepts is very useful in confidently administering a system.

THE NEXT LAYER DOWN

Linux has an extra layer between the filename and the file's actual data on the disk - this is the inode. This has a numerical value which you can see most easily in two ways:

The -i switch on the ls command:

 ls -li /etc/hosts
 35356766 -rw------- 1 root root 260 Nov 25 04:59 /etc/hosts

The stat command:

 stat /etc/hosts
 File: `/etc/hosts'
 Size: 260           Blocks: 8           IO Block: 4096   regular file
 Device: 2ch/44d     Inode: 35356766     Links: 1
 Access: (0600/-rw-------)  Uid: (  0/   root)   Gid: (	0/	root)
 Access: 2012-11-28 13:09:10.000000000 +0400
 Modify: 2012-11-25 04:59:55.000000000 +0400
 Change: 2012-11-25 04:59:55.000000000 +0400

Every file name "points" to an inode, which in turn points to the actual data on the disk. This means that several filenames could point to the same inode - and hence have exactly the same contents. In fact this is a standard technique - called a "hard link". The other important thing to note is that when we view the permissions, ownership and dates of filenames, these attributes are actually kept at the inode level, not the filename. Much of the time this distinction is just theoretical, but it can be very important.

TWO SORTS OF LINKS

Work through the steps below to get familiar with hard and soft linking:

First move to your home directory with:

cd

Then use the ln ("link") command to create a “hard link”, like this:

ln /etc/passwd link1

and now a "symbolic link" (or “symlink”), like this:

ln -s /etc/passwd link2

Now use ls -li to view the resulting files, and less or cat to view them.

Note that the permissions on a symlink generally show as allowing everthing - but what matters is the permission of the file it points to.

Both hard and symlinks are widely used in Linux, but symlinks are especially common - for example:

ls -ltr /etc/rc2.d/*

This directory holds all the scripts that start when your machine changes to “runlevel 2” (its normal running state) - but you'll see that in fact most of them are symlinks to the real scripts in /etc/init.d

It's also very common to have something like :

 prog
 prog-v3
 prog-v4

where the program "prog", is a symlink - originally to v3, but now points to v4 (and could be pointed back if required)

Read up in the resources provided, and test on your server to gain a better understanding. In particular, see how permissions and file sizes work with symbolic links versus hard links or simple files

The Differences

Hard links:

  • Only link to a file, not a directory
  • Can't reference a file on a different disk/volume
  • Links will reference a file even if it is moved
  • Links reference inode/physical locations on the disk

Symbolic (soft) links:

  • Can link to directories
  • Can reference a file/folder on a different hard disk/volume
  • Links remain if the original file is deleted
  • Links will NOT reference the file anymore if it is moved
  • Links reference abstract filenames/directories and NOT physical locations.
  • They have their own inode

EXTENSION

RESOURCES

Some rights reserved. Check the license terms here

12
Day 18 - Log rotation (programming.dev)
 

INTRO

When you’re administering a remote server, logs are your best friend, but disk space problems can be your worst enemy - so while Linux applications are generally very good at generating logs, they need to be controlled.

The logrotate application keeps your logs in check. Using this, you can define how many days of logs you wish to keep; split them into manageable files; compress them to save space, or even keep them on a totally separate server.

Good sysadmins love automation - having the computer automatically do the boring repetitive stuff Just Makes Sense.

ARE YOUR LOGS ROTATING?

Look into your logs directories - /var/log, and subdirectories like /var/log/apache2. Can you see that your logs are already being rotated? You should see a /var/log/syslog file, but also a series of older compressed versions with names like /var/log/syslog.1.gz

WHEN DO THEY ROTATE?

You will recall that cron is generally setup to run scripts in /etc/cron.daily - so look in there and you should see a script called logrotate - or possibly 00logrotate to force it to be the first task to run.

CONFIGURING LOGROTATE

The overall configuration is set in /etc/logrotate.conf - have a look at that, but then also look at the files under the directory /etc/logrotate.d, as the contents of these are merged in to create the full configuration. You will probably see one called apache2, with contents like this:

 /var/log/apache2/*.log {
 weekly
 missingok
 rotate 52
 compress
 delaycompress
 notifempty
 create 640 root adm
 }

Much of this is fairly clear: any apache2 .log file will be rotated each week, with 52 compressed copies being kept.

Typically when you install an application a suitable logrotate “recipe” is installed for you, so you’ll not normally be creating these from scratch. However, the default settings won’t always match your requirements, so it’s perfectly reasonable for you as the sysadmin to edit these - for example, the default apache2 recipe above creates 52 weekly logs, but you might find it more useful to have logs rotated daily, a copy automatically emailed to an auditor, and just 30 days worth kept on the server.

YOUR TASK TODAY

  • Edit your logrotate configuration for apache2 to rotate daily
  • Make whatever other changes you wish
  • Check the next day to see that it’s worked

RESOURCES

Some rights reserved. Check the license terms here

view more: ‹ prev next ›