In Linux, the use of chmod command is to modify a file’s or directory’s permissions. Users can specify the access rights and permissions that a file or directory possesses. The file or directory permissions define who is allowed to read, write, and execute it.
example syntax
chmod [permissions] [File or Directory]Two ways CHMOD COMMAND CAN BE USED:
Octal notation
The permissions are represented in this approach by a 3-digit octal number. The owner’s permissions are represented by the first digit, the group’s permissions by the second, and the others’ permissions by the third. Every digit can have a value between 0 and 7. For instance, the command “chmod 755 file.txt” will grant the owner full permissions (rwx), the group and other users permission to read and execute (r-x).
Symbolic notation
In this approach, a combination of letters and operators is used to indicate the permissions. Read, write, and execute permissions are denoted by the letters r, w, and x, respectively. The operators + and – are used to add and remove permissions respectively whereas, the operator = is used to set permissions. Using the command chmod u+x file.txt for instance, will grant the file’s owner execute permissions (x).
Common flags used with chmod command
- u: This option is used to set the owner of the file or directory’s permissions.
- g: This option is used to modify a file or directory’s permissions for the group.
- o: This option is used to modify a file or directory’s permissions for other users.
- A: The permissions for all users are configured using this option.
- +x: This flag is used to give the file or directory execution permissions.
- +r : This option is used to add read permissions to the file or directory.
- +w : This option is used to add write permissions to the file or directory.
- -x : This option is used to remove execute permissions from the file or directory
“chmod” is one of the most important command and user should have a good knowledge of how to use chmod command. In Linux distributions file permission are very important factor for smooth access and to be able to work properly.
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