usermod [-c comment] [-d home_dir [ -m]] [-g initial_group] [-G group[,...]] [-l login_name] [-p passwd] [-s shell] [-u uid [ -o]] login
specifies the new value of the user's password file comment field.
specifies the user's new login directory. If the -m option is given the contents of the current home directory will be moved to the new home directory, which is created if it does not already exist.
specifies the group name or number of the user's new initial login group. The group name must exist. A group number must refer to an already existing group.
specifies a list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma, with no intervening whitespace. The groups are subject to the same restrictions as the group given with the -g option. If the user is currently a member of a group which is not listed, the user will be removed from the group.
changes the name of the user from login to login_name. Nothing else is changed. In particular, the user's home directory name should probably be changed to reflect the new login name.
is the encrypted password, as returned by crypt(3).
specifies the name of the user's new login shell. Setting this field to blank causes the system to select the default login shell.
specifies the numerical value of the user's ID. This value must be unique, unless the -o option is used. The value must be non-negative. Any files which the user owns and which are located in the directory tree rooted at the user's home directory will have the file user ID changed automatically. Files outside of the user's home directory must be altered manually.