Dec 26, 2023

What are the most important directories in Linux

Working with a Linux distribution is a completely different thing. If you are a windows user you can see they have a drive-based structure for the file systems. If I take an example there is a system directory called C:/windows/system32. If you have another partition they will be D:\, E:\, etc. All the files and folders are inside those drives. So every file path is starting with a drive letter. But in Linux, we treat all things as directories. The directory tree begins with '/'. We call it the root of the tree.

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[email protected]:~$ ls /
0     dev   initrd.img      lib64       mnt   root  snap  tmp  vmlinuz
bin   etc   initrd.img.old  lost+found  opt   run   srv   usr  vmlinuz.old
boot  home  lib

/root and /home directories

Actually, in Linux, there are three things called the root. Above the root of the directory tree is a one. Next, we have a superuser called 'root'. Also, there is a special directory as /root that's owned by the root user. this one is equal to the home folder of the root. Normal users have their own home folders in /home. If your user name is 'us3r' your home folder will be /home/us3r. I think you may have seen that many times there is a flag called root.txt in CTF s inside /root. So if you want to get that flag you need to root the mashing.

/var directory

Here you can find files that have a variable size. It's a common thing that the htdocs folder of the server is located in this directory. In early versions that were/var/www and now that's /var/www/html. Also, log files are located inside this directory. (/var/logs)

[email protected]:~$ ls /var
backups  lib    lock  mail  run   spool  unicornscan
cache    local  log   opt   snap  tmp    www

/tmp directory

This is the place for temporary files. Usually, this folder has written permission for all. You may find that when uploading a shell to the server we first change the current directory to /tmp.

/sys /usr directory

This directory comes with commands and data files. There are many sub-application files in /usr/share folder.

[email protected]:~$ ls /usr
bin  games  include  lib  lib64  local  sbin  share  src  var

[email protected]:~$ ls /usr/share
accountsservice              gvfs                            pev
aclocal                      hal                             php7.2-common
aclocal-1.16                 hamster-sidejack                php7.2-json
adduser                      hashcat                         php7.2-mysql
afl                          hashcat-utils                   php7.2-opcache
aglfn                        help                            php7.2-pgsql
airgeddon                    hexorbase                       php7.2-readline
alsa                         hfsprogs                        php7.2-sqlite3
android-framework-res        highlight                       pipal
ant                          homebank                        pixmaps

/etc directory

This folder is responsible for holding all configuration files. If you want to tweak your Is or programs you may need to go there. For example to change sources in apt you want to edit /etc/sources.d

[email protected]:~$ ls /etc
adduser.conf            gimp                  menu-methods       rmt
adjtime                 glvnd                 mercurial          rpc
aliases                 gnome-system-tools    mime.types         rsyslog.conf
alsa                    gnuradio              miredo             rsyslog.d
alternatives            groff                 miredo.conf        samba
amap                    group                 mke2fs.conf        sane.d
anonsurf                group-                modprobe.d         scalpel
apache2                 grub.d                modules            screenrc
apm                     gshadow               modules-load.d     securetty
apparmor                gshadow-              mono               security
apparmor.d              gss                   motd               selinux
apt                     gtk-2.0               mpv                sensors3.conf
arpwatch                gtk-3.0               mtab               sensors.d

/bin directory

This directory contains all executable binary files required for booting the system. Commands those run in single user-mode such as ls, ping, chmod are also located here.

[email protected]:~$ ls /bin
bash                findmnt         netstat        su
btrfs               fsck.btrfs      networkctl     sync
btrfsck             fuser           nisdomainname  systemctl
btrfs-find-root     fusermount      ntfs-3g        systemd
btrfs-image         getfacl         ntfs-3g.probe  systemd-ask-password
btrfs-map-logical   grep            ntfscat        systemd-escape
btrfs-select-super  gunzip          ntfscluster    systemd-hwdb

/lib directory

Here you can find system libraries and kernel modules.

/opt directory

This folder can be used to hold custom program files. If you wanted to install sublime manually you may copy files to /opt/sublime.

[email protected]:~$ ls /opt
car-hacking  firmware-mod-kit  sublime_text  Teeth  xplico

/dev directory

This directory contains device-related files for all hardware devices. If you are going to mount a new drive you may need this directory.

[email protected]:~$ ls /dev
agpgart          kmsg                serial    tty20  tty47    uhid
autofs           log                 sg0       tty21  tty48    uinput
block            loop-control        sg1       tty22  tty49    urandom
bsg              lp0                 sg2       tty23  tty5     vcs
btrfs-control    mapper              sg3       tty24  tty50    vcs1
bus              mem                 sg4       tty25  tty51    vcs2
cdc-wdm0         memory_bandwidth    shm       tty26  tty52    vcs3
cdrom            mqueue              snapshot  tty27  tty53    vcs4
cdrw             net                 snd       tty28  tty54    vcs5

So I hope you got an idea about the Linux directory tree. Thank you for reading. Just leave a comment if something is unclear or wrong.