📂File System
The linux file system is mostly the same between different distributions. Certain directories are for certain things. Let's look at it in detail.
Categories
With two metrics, we can categorize the directories:
Whether the data is changing often or not
Whether the data is shared between different hosts or not
Filesystem Hierarchy Standard
FHS is a stamdard that tells which directory should contain what. It is followed by most linux distributions.
Directories
| Directory | Description |
|---|---|
/ | Primary directory of the entire filesystem hierarchy |
/bin | Essential executable programs that must be available in single user mode |
/boot | Files needed to boot the system, such as the kernel, initrd or initramfs images, and boot configuration files and |
/dev | Device Nodes, used to interact with hardware and software devices |
/etc | System-wide configuration files |
/home | User home directories, including personal settings, files, etc. |
/lib | Libraries required by executable binaries in /bin and /sbin |
/lib64 | 64-bit libraries required by executable binaries in /bin and /sbin, for systems which can run both 32-bit and |
/media | Mount points for removable media such as CDs, DVDs, USB sticks, etc. |
/mnt | Temporarily mounted filesystems |
/opt | Optional application software packages |
/proc | Virtual pseudo-filesystem giving information about the system and processes running on it. Can be used to alter |
/run | Run-time variable data, containing information describing the system since it was booted. Replaces the older /var/run |
/sys | Virtual pseudo-filesystem giving information about the system and processes running on it. Can be used to alter |
/root | Home directory for the root user |
/sbin | Essential system binaries |
/srv | Site-specific data served up by the system. Seldom used. |
/tmp | Temporary files; on many distributions lost across a reboot and may be a ramdisk in memory. |
/usr | Multi-user applications, utilities and data; theoretically read-only. |
/var | Variable data that changes during system operation |
/ | Used for misc. files |
/ | Used for booting tftp |
/bin & /sbin
Contains executables and scripts.
Required files: cat, chgrp, chmod, chown, cp, date, dd, df, dmesg, echo, false, hostname, kill, ln, login, ls, mkdir, mknod, more, mount, mv, ps, pwd, rm, rmdir, sed, sh, stty, su, sync, true, umount and uname
Optional files: test, csh, ed, tar, cpio, gunzip, zcat, netstat and ping
Recent versions of Linux distributions have abandoned /usr/bin and /bin distinction. They are now merged into /usr/bin. Same goes for /usr/sbin and /sbin.
Required for /sbin: fdisk, fsck, getty, halt, ifconfig, init, mkfs, mkswap, reboot, route, swapon, swapoff, update.
/boot
Required files: vmlinuz (compressed linux kernel), initramfs (initial RAM filesystem)
Optional files: config (configure kernal compilation), System.map (debugging symbols for the kernel)
Instead of initramfs, some distributions use initrd (initial RAM disk). They are similar.
/dev
It has device nodes.
/etc
System-wide configuration files.
Required files: csh.login, exports, fstab, ftpusers, gateways, gettydefs, group, host.conf, hosts.allow, hosts.deny, hosts.equiv, hosts.lpd, inetd.conf, inittab, issue, ld.so.conf, motd, mtab, mtools.conf, networks, passwd, printcap, profile, protocols, resolv.conf, rpc, securetty, services, shells, syslog.conf.
Some of these files are obsolete and not used anymore. (eg. mtools.conf)
Red Hat based distributions have /etc/sysconfig directory. It contains configuration files for various services.
Important Subdirectories
It has skeleton/template files for new home directories
/home & /root
/home/username is the home directory for the user username.
This directory is added to $HOME environment variable and is available as ~ in the shell.
/lib & /lib64
Libraries required by executables in /bin and /sbin.
/media
Mount points for removable media such as CDs, DVDs, USB sticks, etc.
/mnt
Mount points for temporarily mounted filesystems.
/opt
For software that would like to be isolated from the rest of the system. It is not used much.
/proc (Process Information Pseudo-filesystem)
Virtual filesystem that provides information about the system and processes running on it.
/sys (System Information Pseudo-filesystem)
Virtual filesystem that provides information about the system and processes running on it. Similar to a device tree and is part of the Unified Device Model.
/srv (Service Data)
Site-specific data served up by the system.
/tmp (Temporary Files)
Temporary files; on many distributions lost across a reboot and may be a ramdisk in memory.
/usr (Unix System Resources)
Multi-user applications, utilities and data; theoretically read-only.
/var (Variable Data)
Variable data that changes during system operation.
/run (Run-time Variable Data)
Stores transient files that are not needed across reboots. It is a replacement for /var/run and /var/lock.
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