knowledge/technology/linux/Linux.md

---
obj: os
wiki: https://en.wikipedia.org/wiki/Linux
website: https://www.kernel.org
---

# Linux
Linux is a kernel and computing platform.
It support virtually every [filesystem](filesystems/Filesystems.md). Linux has many distributions, such as [Arch Linux](Arch%20Linux.md) or [Alpine Linux](Alpine%20Linux.md), [Proxmox](Proxmox.md), etc.
The default init system is [Systemd](systemd/Systemd.md). See [mkinitcpio](mkinitcpio.md) for other boot time configuration.
Linux has GUIs but is generally used with the [Shell](../applications/cli/Shell.md). The kernel development can be tracked [here](https://kernel.org)

## Filesystem Structure
A typical Linux system has, among others, the following directories:

| Path             | Description                                                                                                                                                                                                                                                            |
| ---------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `/`              | This is the root directory. This is where the whole tree starts.                                                                                                                                                                                                       |
| `/bin`           | This directory contains executable programs which are needed in single user mode and to bring the system up or repair it.                                                                                                                                              |
| `/boot`          | Contains static files for the boot loader. This directory holds only the files which are needed during the boot process. The operating system kernel (initrd for example) must be located in either `/` or `/boot`.                                                    |
| `/dev`           | Special or device files, which refer to physical devices.                                                                                                                                                                                                              |
| `/etc`           | Contains configuration files which are local to the machine.                                                                                                                                                                                                           |
| `/home`          | On machines with home directories for users, these are usually beneath this directory, directly or not.                                                                                                                                                                |
| `/lib`           | This directory should hold those shared libraries that are necessary to boot the system and to run the commands in the root filesystem.                                                                                                                                |
| `/lib/modules`   | Loadable kernel modules (optional)                                                                                                                                                                                                                                     |
| _`/lost+found`_  | This comes from [Ext4](filesystems/Ext4.md). This directory contains items lost in the filesystem.                                                                                                                                                                     |
| `/media`         | This directory contains mount points for removable media such as CD and DVD disks or USB sticks.                                                                                                                                                                       |
| `/mnt`           | This directory is a mount point for a temporarily mounted filesystem.                                                                                                                                                                                                  |
| `/proc`          | This is a mount point for the _proc_ filesystem, which provides information about running processes and the kernel.                                                                                                                                                    |
| `/root`          | This directory is usually the home directory for the root user (optional).                                                                                                                                                                                             |
| `/run`           | This directory contains information which describes the system since it was booted. Once this purpose was served by `/var/run` and programs may continue to use it.                                                                                                    |
| `/sbin`          | Like `/bin`, this directory holds commands needed to boot the system, but which are usually not executed by normal users.                                                                                                                                              |
| `/sys`           | This is a mount point for the _sysfs_ filesystem, which provides information about the kernel like _/proc_, but better structured, following the formalism of kobject infrastructure.                                                                                  |
| `/tmp`           | This directory contains temporary files which may be deleted with no notice, such as by a regular job or at system boot up.                                                                                                                                            |
| `/usr`           | This directory is usually mounted from a separate partition. It should hold only shareable, read-only data, so that it can be mounted by various machines running Linux.                                                                                               |
| `/usr/bin`       | This is the primary directory for executable programs. Most programs executed by normal users which are not needed for booting or for repairing the system and which are not installed locally should be placed in this directory.                                     |
| `/usr/etc`       | Site-wide configuration files to be shared between several machines may be stored in this directory. However, commands should always reference those files using the `/etc` directory. Links from files in `/etc` should point to the appropriate files in `/usr/etc`. |
| `/usr/include`   | Include files for the C compiler.                                                                                                                                                                                                                                      |
| `/usr/lib`       | Object libraries, including dynamic libraries, plus some executables which usually are not invoked directly. More complicated programs may have whole subdirectories there.                                                                                            |
| `/usr/share`     | This directory contains subdirectories with specific application data, that can be shared among different architectures of the same OS.                                                                                                                                |
| `/usr/share/doc` | Documentation about installed programs (optional).                                                                                                                                                                                                                     |
| `/usr/share/man` | [Manual pages](../applications/cli/system/man.md) go here in subdirectories according to the man page sections.                                                                                                                                                        |
| `/var`           | This directory contains files which may change in size, such as spool and [log](../dev/Log.md) files.                                                                                                                                                                  |
| `/var/cache`     | Data cached for programs.                                                                                                                                                                                                                                              |
| `/var/log`       | Miscellaneous [log](../dev/Log.md) files.                                                                                                                                                                                                                              |