oreilly.comSafari Books Online.Conferences.


Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

Buy it now, or read it online on Safari Bookshelf.


usermod [options] user

System administration command. Modify user account information.


-c comment

Comment field.

-d dir

Home directory.

-e date

Account expiration date. date is in the format MM/DD/YYYY; two-digit year fields are also accepted. The value is stored as the number of days since January 1, 1970. This option requires the use of shadow passwords.

-f days

Permanently disable account this many days after the password has expired. A value of -1 disables this feature. This option requires the use of shadow passwords.

-g group

Initial group name or number.

-G groups

Supplementary groups given by name or number in a comma-separated list with no whitespace. user will be removed from any groups to which it currently belongs that are not included in groups.

-l name

Login name. This cannot be changed while the user is logged in.


Lock user's password by putting a ! in front of it. This option cannot be used with -p or -U.


Override. Accept a nonunique uid with the -u option.

-p pw

Encrypted password, as returned from crypt(3).

-s shell

Login shell.

-u uid

Numerical user ID. The value must be unique unless the -o option is used. Any files owned by user in the user's home directory will have their user ID changed automatically. Files outside of the home directory will not be changed. user should not be executing any processes while this is changed.


Unlock the user's password by removing the ! that -L put in front of it. This option cannot be used with -p or -L.

Linux Resources
  • Linux Online
  • The Linux FAQ
  • Linux Kernel Archives
  • Kernel Traffic

  • Sponsored by: