I. Linux Directory Structure
Do you want to know why some programs are located under /bin, or /sbin, or /usr/bin, or /usr/sbin? For example, the less command is located under /usr/bin. Why isn’t it in /bin, or /sbin, or /usr/sbin? What are the differences between all these directories?
In this article, let’s review the Linux filesystem structure and understand the meaning of each top-level directory.
Blue: indicates a directory
Cyan: indicates a link
Black: indicates a file
1. / – Root
Every file and directory starts from the root directory.
Only the root user has write permission in this directory. Note that /root is the home directory of the root user, which is different from /.
2. /bin – User binaries
Contains binary executable files.
The common Linux commands you need to use in single-user mode are located in this directory. Commands used by all users of the system are placed here.
For example: ps, ls, ping, grep, cp
3. /sbin directory – System binaries
Like /bin, /sbin also contains binary executable files.
However, the Linux commands in this directory are typically used by the system administrator for system maintenance. For example: iptables, reboot, fdisk, ifconfig, swapon
4. /etc – Configuration files
Contains all the configuration files required by programs.
It also contains startup and shutdown shell scripts used to start/stop individual programs. For example: /etc/resolv.conf, /etc/logrotate.conf
hosts: resolves device names (or domain names) to IP addresses, equivalent to a locally available DNS function. See the images below:
5. /dev – Device files
Contains device files.
These include terminal devices, USB devices, or any devices connected to the system. For example: /dev/tty1, /dev/usbmon0
6、/proc – Process information
Contains information related to system processes.
This is a virtual file system that contains information about running processes. For example, the /proc/{pid} directory contains information related to a specific pid.
This is a virtual file system where system resources are represented as text information. For example: /proc/uptime
7、/var – Variable files
var stands for variable files.
This directory contains files whose contents may grow.
These include –
system log files (/var/log); package and database files (/var/lib); email (/var/mail); print queues (/var/spool); lock files (/var/lock); temporary files needed across multiple reboots (/var/tmp);
8、/tmp – Temporary files
Contains temporary files created by the system and users.
When the system restarts, all files in this directory will be deleted.
9、/usr – User programs
Contains binary files, libraries, documentation, and source code for secondary programs.
/usr/bin contains binary files for user programs. If you can’t find a user binary in /bin, look in the /usr/bin directory. For example: at, awk, cc, less, scp.
/usr/sbin contains binary files for system administrators. If you can’t find a system binary in /sbin, look in the /usr/sbin directory. For example: atd, cron, sshd, useradd, userdel.
/usr/lib contains the libraries used by /usr/bin and /usr/sbin.
/usr/local contains user programs installed from source. For example, when you install Apache from source, it will be in /usr/local/apache2.
10、/home – HOME directory
All users use the home directory to store their personal files.
For example: /home/john, /home/nikita
11、/boot – Boot loader files
Contains files related to the boot loader.
The kernel’s initrd, vmlinux, and grub files are located under /boot.
For example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic
12、/lib – System libraries
Contains library files that support the binary files located under /bin and /sbin.
Library file names are ld* or lib*.so.*
For example: ld-2.11.1.so, libncurses.so.5.7
13、/opt – Optional add-on applications
opt stands for optional.
Contains add-on applications from individual vendors.
Add-on applications should be installed in /opt/ or in subdirectories under /opt/.
14、/mnt – Mount directory
A temporary mount directory where the system administrator can mount file systems.
15、/media – Removable media devices
A temporary directory used for mounting removable devices.
For example, /media/cdrom for mounting a CD-ROM, and /media/floppy for mounting a floppy drive;
16、/srv – Service data
srv stands for service.
Contains data related to site-specific services provided by the server.
For example, /srv/cvs contains data related to cvs.
[Reference]
Linux Filesystem Hierarchy
Source and pre-formatted versions available 1. Linux
Filesystem Hierarchy
- 1.1. Foreward
- 1.2. The Root Directory
- 1.3. /bin
- 1.4. /boot
- 1.5. /dev
- 1.6. /etc
- 1.7. /home
- 1.8. /initrd
- 1.9. /lib
- 1.10. /lost+found
- 1.11. /media
- 1.12. /mnt
- 1.13. /opt
- 1.14. /proc
- 1.15. /root
- 1.16. /sbin
- 1.17. /usr
- 1.18. /var
- 1.19. /srv
- 1.20. /tmp
Glossary A. UNIX System V Signals B. Sources C. About the
Author D. Contributors E. Disclaimer F. Donations G. Feedback H. GNU
Free Documentation License
- H.1. PREAMBLE
- H.2. APPLICABILITY AND DEFINITIONS
- H.3. VERBATIM COPYING
- H.4. COPYING IN QUANTITY
- H.5. MODIFICATIONS
- H.6. COMBINING DOCUMENTS
- H.7. COLLECTIONS OF DOCUMENTS
- H.8. AGGREGATION WITH INDEPENDENT WORKS
- H.9. TRANSLATION
- H.10. TERMINATION
- H.11. FUTURE REVISIONS OF THIS LICENSE
- H.12. ADDENDUM: How to use this License for your documents
II. Common Commands
1. Command Help
2. Users
3. SHELL
4. Display hard drive, partition, CPU, and memory information
5. Network
6. Processes
7. Files
- 1. Command Help
-
[[email protected]
~]#man ps 
- 2. Users
-
$finger username Displays information about user username
$who Displays currently logged-in users
$who am I
$su Become the root user
$sudo command Execute as the root user
$passwd Change password 
- 3. SHELL
-
$history Displays command history in the current shell
$alias Displays all command aliases
$alias new_command=’command’
Alias command as new_command
$env Displays all environment variables
$export var=value Sets environment variable var to value 
- 4. Display hard disk, partition, CPU, and memory information
- $df -lh Displays usage status of all hard disks
-
$du -sh *
Displays the size of each directory and file in the current directory -
-
$mount Displays all mounted disk partitions
$mount partition path Mounts partition to path
$umount partition Unmounts partition
$sudo fdisk -l Displays all partitions
$sudo fdisk device
Creates a partition table for device (for example /dev/sdc). After entering, choose n, p, w
$sudo mkfs -t ext3 partition
Formats partition patition (for example /dev/sdc1)
Modify /etc/fstab to automatically mount the partition. Add the line:
/dev/sdc1 path(mount point) ext3 defaults 0 0
$arch Displays architecture
$cat /proc/cpuinfo Displays CPU information
$cat /proc/meminfo Displays memory information
$free Displays memory usage 
- 5. Network
-
$ifconfig
Displays network interfaces and their corresponding IP addresses. ifconfig can also be used to configure network interfaces
$ifup eth0 Starts the eth0 interface
$ifdown eth0 Shuts down the eth0 interface
$iwconfig Displays wireless network interfaces
$route Displays the routing table. route can also be used to modify the routing table
$netstat Displays the current network connection status
$ping IP Sends ping packets to address IP
$traceroute IP Traces the route path to address IP
$dhclient
Sends a DHCP request to a DHCP host to obtain an IP address and other configuration information.
$host domain DNS lookup, finds the IP corresponding to domain name domain
$host IP Reverse DNS lookup
$wget url Uses wget to download the resource pointed to by url
$wget -m url Mirror download 
- 6. Processes
-
$top Displays process information and updates in real time
$ps Displays processes in the current shell
$ps -lu username Displays processes for user username
$ps -ajx Displays all processes in a more complete format
$kill PID Kills process PID (PID is the Process ID) 
- 7. Files
-
$touch filename
If the file does not exist, creates an empty file; if the file exists, updates the file access and modification times.
$rm filename Deletes a file
$cp file1 file2 Copies file1 to file2
$ls -l path Displays files and related file information
$mkdir dir Creates directory dir
$mkdir -p path Recursively creates all directories in path
$rmdir dir Deletes directory dir; dir must be empty.
$rm -r dir Deletes directory dir and all files it contains
$file filename Type description of file filename
$chown username:groupname filename
Changes the file owner to owner and the group to group
$chmod 755 filenameChanges the file permissions to 755: owner r+w+x,
group: r+x, others: r+x
$od -c filename Displays the file as ASCII characters
$cat filename Displays a file
$cat file1 file2 Displays file1 and file2 concatenated
$head -1 filename Displays the first line of the file
$tail -5 filename Displays the fifth line from the end of the file
$diff file1 file2 Displays the differences between file1 and file2
$sort filename Sorts the lines in the file and displays them
$sort -f filename Sorts without considering case
$sort -u filename Sorts and removes duplicate lines
$uniq filename Displays non-repeated lines in file filename
(lines with identical content but not adjacent are not considered duplicates)
$wc filename Counts characters, words, and lines in the file
$wc -l filename Counts the number of lines in the file
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