Linux chmod Command

The chmod command sets the permissions of files or directories.

chmod <options> <permissions> <file name>
sudo chmod -R 755 /var/www/my_website

There are two ways to represent permissions

  • Octal numbers (the digits 0, 1, 2, 4, 5, and 7)
  • Symbols (alphanumeric characters)

Octal numbers

Octal permissions notation uses a pattern of three single-digit numbers to define all permissions. The single digit numbers 0, 1, 2, 4, 5, and 7 used are. 3 and 6 are not used.

0 stands for “no permission.”
1 stands for “execute”.
2 stands for “write”.
4 stands for “read”.
5 stands for “read and execute” and is the combination of permissions 1+4.
7 stands for “read, write, and execute” and is the combination of permissions 1+2+4.


u stands for user.
g stands for group.
o stands for others.
a stands for all.

A combination of the letters ugoa controls which users’ access to the file will be changed: the user who owns it u, other users in the file’s group g, other users not in the file’s group o, or all users a. If none of these are given, the effect is as if a were given, but bits that are set in the umask are not affected.

That means that chmod u+x somefile will grant only the owner of that file execution permissions whereas chmod +x somefile is the same as chmod a+x somefile.

The format of a symbolic mode is [ugoa...][[+-=][rwxXstugo...]...][,...]. Multiple symbolic operations can be given, separated by commas.

More Resources