Provided by:
passwd_4.0.18.2-1ubuntu2_i386 
NAME
usermod - modify a user account
SYNOPSIS
usermod [options] LOGIN
DESCRIPTION
The usermod command modifies the system account files to reflect the
changes that are specified on the command line.
OPTIONS
The options which apply to the usermod command are:
-a, --append
Add the user to the supplemental group(s). Use only with -G option.
-c, --comment COMMENT
The new value of the user´s password file comment field. It is
normally modified using the chfn(1) utility.
-d, --home HOME_DIR
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.
-e, --expiredate EXPIRE_DATE
The date on which the user account will be disabled. The date is
specified in the format YYYY-MM-DD.
-f, --inactive INACTIVE
The number of days after a password expires until the account is
permanently disabled. A value of 0 disables the account as soon as
the password has expired, and a value of -1 disables the feature.
The default value is -1.
-g, --gid GROUP
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. The default group number is 1.
-G, --groups GROUP1[,GROUP2,...[,GROUPN]]]
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. This behaviour can be changed via the -a
option, which appends the user to the current supplementary group
list.
-l, --login NEW_LOGIN
The name of the user will be changed from LOGIN to NEW_LOGIN.
Nothing else is changed. In particular, the user´s home directory
name should probably be changed manually to reflect the new login
name.
-L, --lock
Lock a user´s password. This puts a ´!´ in front of the encrypted
password, effectively disabling the password. You can´t use this
option with -p or -U.
-o, --non-unique
When used with the -u option, this option allows to change the user
ID to a non-unique value.
-p, --password PASSWORD
The encrypted password, as returned by crypt(3).
-s, --shell SHELL
The name of the user´s new login shell. Setting this field to blank
causes the system to select the default login shell.
-u, --uid UID
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.
Values between 0 and 999 are typically reserved for system
accounts. 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.
-U, --unlock
Unlock a user´s password. This removes the ´!´ in front of the
encrypted password. You can´t use this option with -p or -L.
CAVEATS
usermod will not allow you to change the name of a user who is logged
in. You must make certain that the named user is not executing any
processes when this command is being executed if the user´s numerical
user ID is being changed. You must change the owner of any crontab
files manually. You must change the owner of any at jobs manually. You
must make any changes involving NIS on the NIS server.
FILES
/etc/group
Group account information.
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
SEE ALSO
chfn(1), chsh(1), passwd(1), crypt(3), gpasswd(8), groupadd(8),
groupdel(8), groupmod(8), login.defs(5), useradd(8), userdel(8).