linux/README.md

Linux

Filesystem

Types

• ext4
• btrfs
• zfs
• xfs

Structure

$ ls -l
/bin
/boot
/dev
/etc
/home
/lib
/media
/mnt
/opt
/run
/sbin
/srv
/tmp
/proc
/sys
/var
/lost+found
/root
/usr

• / - This is the beginning of the Linux filesystem hierarchy. All the file paths originate from the root.
  • /bin - Stores essential command binaries which can be used by both system administrator and the user such as cat,ls,mv,ps,mount etc.
  • /boot - This directory contains all the files necessary for the system to boot up
  • /dev - Contains device files for all the physical and virtual devices mounted in the system.
  • /etc - This directory contains configuration files of your system.
  • /home - The home contains all the personal user-specific files. It contains separate directories for each user which can be accessed by cd /home/username
  • /lib - Libraries are standard code files that define the commands used in a programming language. During compilation, a compiler looks up these libraries to make sense of the code just as we might look up a dictionary to understand the meaning of words while reading a book.
  • /media - This directory contains several sub-directories where the system mounts removable devices such as USB drives.
  • /mnt - This directory can be used by a user to manually mount a device. (as opposed to /media which is only used by the system)
  • /opt - Cntains libraries and binaries related to packages which are not installed by your system’s package managers but are installed through third-party means like using Discord’s in-application update button.
  • /run - This directory contains the metadata of the device since the last boot. This includes data of all the system processes and daemons that were executed in the current session. Files under this directory are cleared (removed or truncated) at the beginning of the boot process.
  • /sbin - Just like /bin, /sbin also contains essential system binaries. However, these binaries are only meant to be used by a system administrator rather than a normal user. These binaries are mostly used for device management. For example, fdisk, fsck, mkfs, ifconfig, reboot.
  • /srv - You will only ever use this directory if your device is acting as a webserver, as this directory contains all the files regarding web servers.
  • /tmp - Contains temporary files of the currently running processes. This data is also flushed after every boot.
  • /proc - Just like /dev which provides devices as files, this folder contains system information and kernel information as files.
  • /sys- It contains information similarly held in /proc/, but displays a hierarchical view of specific device information in regards to hot-plug devices.
  • /var - Contains variable data regarding the running processes. This includes the logs, cache and spools for all applications.
  • /lost+found (ext4 feature) - While not listed in the FHS, this directory is automatically generated by fsck.
  • /root - This is supposed to be the home directory for the root user, as opposed to /home which is the home directory for the non-root users.
  • /usr - The /usr directory has very interesting origins. At the time of formation, it was supposed to act like the /home directory, but when people ran out of space on /bin, they started storing the non-essential binaries in /usr. You can read the whole story here.

Mounting

Attributes

Owneship attributes

• user
• group
• other

Shell

Types

Shortcuts

Processes

Foreground & background

Services & systemd

Administration

Installing software

packages

archives

source

Applications

tmux

vim

Commands

ls

Lists files

ls /
afs  bin  boot  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

ls -la /
total 20
dr-xr-xr-x.   1 root root  170 Nov 14 16:18 .
dr-xr-xr-x.   1 root root  170 Nov 14 16:18 ..
dr-xr-xr-x.   1 root root    0 Aug  9 15:57 afs
lrwxrwxrwx.   1 root root    7 Aug  9 15:57 bin -> usr/bin
dr-xr-xr-x.   7 root root 4096 Nov 14 16:25 boot
drwx------.   1 root root    0 Aug 30 04:57 .cache
drwxr-xr-x.  21 root root 3880 Jan  3 20:37 dev
drwxr-xr-x.   1 root root 5706 Jan  3 20:37 etc
drwxr-xr-x.   1 root root   22 Aug  9 15:57 home
lrwxrwxrwx.   1 root root    7 Aug  9 15:57 lib -> usr/lib
lrwxrwxrwx.   1 root root    9 Aug  9 15:57 lib64 -> usr/lib64
drwx------.   1 root root    0 Apr 23  2021 lost+found
drwxr-xr-x.   1 root root    0 Aug  9 15:57 media
drwxr-xr-x.   1 root root    0 Aug  9 15:57 mnt
drwxr-xr-x.   1 root root   42 Aug  9 15:57 opt
dr-xr-xr-x. 295 root root    0 Jan  3 20:36 proc
dr-xr-x---.   1 root root  574 Dec 27 22:01 root
drwxr-xr-x.  62 root root 1640 Jan  3 20:39 run
lrwxrwxrwx.   1 root root    8 Aug  9 15:57 sbin -> usr/sbin
drwxr-xr-x.   1 root root    0 Aug  9 15:57 srv
dr-xr-xr-x.  13 root root    0 Jan  3 20:36 sys
drwxrwxrwt.  20 root root  460 Jan  6 21:18 tmp
drwxr-xr-x.   1 root root  202 Dec 26 21:31 usr
drwxr-xr-x.   1 root root  200 Jan  3 20:37 var

• cd -

• cat -

• tac -

• more -

• less -

• cut -

• head -

• tail -

• diff -

• wc -

• grep -

• find -

• chmod -

• chown -

• chmod -

• rm -

• rmdir -

• touch -

• mkdir -

• ln -

• cp -

• mv -

• tar -

• gzip -

• zip -

• unzip -

• du -

• df -

• mount -

• umount -

• sed -

• history -

• sudo -

• su -

• passwd -

• passwd -

• ps -

• top -

• htop -

• which -

• kill -

• bg -

• fg -

• disown -

• sleep -

• lscpu -

• wall -

• shutdown -

• reboot -

• halt -

• ss -

• dig -

• curl -

• wget -

• ssh -

• tmux -