📖 Guide

Chmod — Complete Reference

Linux file permission commands and patterns for chmod.

47 commands across 7 categories

Numeric Mode Symbolic Mode Common Permissions Directory Permissions Special Permissions Recursive Common Patterns

Numeric Mode

Command	Description
`chmod 755 file`	Owner rwx, group rx, others rx
`chmod 644 file`	Owner rw, group r, others r
`chmod 700 file`	Owner rwx, no access for others
`chmod 600 file`	Owner rw only, no access for others
`chmod 777 file`	Full permissions for everyone (use with caution)
`chmod 000 file`	Remove all permissions
`chmod 750 file`	Owner rwx, group rx, others none

Symbolic Mode

Command	Description
`chmod u+x file`	Add execute permission for owner
`chmod g+w file`	Add write permission for group
`chmod o-r file`	Remove read permission for others
`chmod a+r file`	Add read permission for all (user, group, others)
`chmod u=rwx,g=rx,o=r file`	Set exact permissions for each class
`chmod ug+x file`	Add execute for owner and group
`chmod u+x,g-w,o-rwx file`	Multiple changes in one command

Common Permissions

Command	Description
`chmod 644 file.txt`	Standard file: owner rw, others read-only
`chmod 755 script.sh`	Executable script: owner rwx, others rx
`chmod 600 ~/.ssh/id_rsa`	SSH private key: owner rw only
`chmod 644 ~/.ssh/id_rsa.pub`	SSH public key: owner rw, others read
`chmod 400 secret.pem`	Read-only for owner, no access for others
`chmod 664 shared.txt`	Owner and group rw, others read-only

Directory Permissions

Command	Description
`chmod 755 dir/`	Standard directory: owner full, others can list and enter
`chmod 700 dir/`	Private directory: only owner can access
`chmod 750 dir/`	Group-accessible directory: owner full, group can list/enter
`chmod 1777 /tmp`	World-writable with sticky bit (like /tmp)
`chmod 2775 dir/`	Setgid directory: new files inherit group ownership
`chmod o+x dir/`	Allow others to enter directory (requires r to list)

Special Permissions

Command	Description
`chmod u+s file` e.g. chmod u+s /usr/bin/passwd	Set SUID — file executes as the file owner
`chmod g+s file`	Set SGID — file executes with group privileges
`chmod g+s dir/`	Set SGID on directory — new files inherit group
`chmod +t dir/`	Set sticky bit — only owner can delete their files
`chmod 4755 file` e.g. ls -l shows -rwsr-xr-x	Numeric SUID: 4xxx prefix
`chmod 2755 file` e.g. ls -l shows -rwxr-sr-x	Numeric SGID: 2xxx prefix
`chmod 1755 dir/` e.g. ls -l shows drwxr-xr-t	Numeric sticky bit: 1xxx prefix

Recursive

Command	Description
`chmod -R 755 dir/`	Apply permissions recursively to directory and contents
`chmod -R u+w dir/`	Add write permission recursively for owner
`find dir/ -type f -exec chmod 644 {} +`	Set 644 on files only (not directories)
`find dir/ -type d -exec chmod 755 {} +`	Set 755 on directories only (not files)
`chmod -R a-x,a+X dir/`	Remove execute from files, keep on directories
`chmod -R g=u dir/`	Make group permissions match owner recursively

Common Patterns

Command	Description
`chmod +x script.sh`	Make a script executable
`chmod -R 755 /var/www/html`	Web server document root permissions
`chmod 600 .env`	Protect environment/config files
`chmod 700 ~/.ssh`	Secure SSH directory
`chmod 644 ~/.ssh/authorized_keys`	SSH authorized keys file
`stat -c '%a %n' file`	View current numeric permissions of a file
`ls -la`	List files with permissions in symbolic format
`umask 022`	Set default permissions for new files (results in 644/755)

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