chmod / chown / chgrp

chmod [options] mode file
chown [options] user[:group] file
chgrp [options] group file

Command / Notation	Description
chmod 755 file	Sets permissions using octal notation (7=rwx, 5=r-x).
chmod +x file	Adds execute permission for all users.
chmod u+x file	Adds execute permission for the file owner (user).
chmod g-w file	Removes write permission from the group.
chmod o=r file	Sets permissions for others to read-only.
chmod -R mode directory	Recursively changes permissions for a directory and its contents.
chown user file	Changes the owner of a file.
chown user:group file	Changes both the owner and group at once.
chown -R user directory	Recursively changes the owner for a directory and its contents.
chgrp group file	Changes only the group of a file.

The following examples use this directory structure.

Add execute permission to a script. This is the most common use case.

chmod +x deploy.sh
ls -l deploy.sh
-rwxr-xr-x 1 user staff 128 Mar  5 10:00 deploy.sh

Set permissions using octal notation. This sets owner to read/write/execute (7), group to read-only (4), and no access for others (0).

chmod 740 secret.conf
ls -l secret.conf
-rwxr----- 1 user staff 256 Mar  5 10:00 secret.conf

Set standard web server permissions.

chmod 644 public/index.html
ls -l public/index.html
-rw-r--r-- 1 user staff 2048 Mar  5 10:00 public/index.html

chmod 755 public/
ls -ld public/
drwxr-xr-x 2 user staff 4096 Mar  5 10:00 public/

Change permissions for all files in a directory at once.

chmod -R 755 public/

Change the owner and group together (requires root privileges).

sudo chown www-data:www-data /var/www/html
ls -ld /var/www/html
drwxr-xr-x 5 www-data www-data 4096 Mar  5 10:00 /var/www/html

Recursively change the owner for a directory and all its contents.

sudo chown -R deploy:deploy /var/www/app

Octal permission notation is the sum of 4=read (r), 2=write (w), and 1=execute (x). For example, rwxr-xr-x is 755 (7=4+2+1, 5=4+0+1). You can use either symbolic notation (u/g/o with +/-/=) or octal notation — both work, but octal is more explicit and easier to read in scripts.

You can check a file's current permissions and owner with $ ls -l. For detailed metadata, see stat.