- The usermod command modifies the system account files to reflect the changes that are specified on the command line
usermod [options] LOGIN
-a, --append Add the user to the supplementary group(s). Use only with the -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. If the current home directory does not exist the new home directory will not be created. -e, --expiredate EXPIRE_DATE The date on which the user account will be disabled. The date is specified in the format YYYY-MM-DD. An empty EXPIRE_DATE argument will disable the expiration of the account. This option requires a /etc/shadow file. A /etc/shadow entry will be created if there were none. -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. This option requires a /etc/shadow file. A /etc/shadow entry will be created if there were none. -g, --gid GROUP The group name or number of the user´s new initial login group. The group must exist. Any file from the user´s home directory owned by the previous primary group of the user will be owned by this new group. The group ownership of files outside of the user´s home directory must be fixed manually. -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 or mail spool should probably be renamed 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. Note: if you wish to lock the account (not only access with a password), you should also set the EXPIRE_DATE to 1. -m, --move-home Move the content of the user´s home directory to the new location. If the current home directory does not exist the new home directory will not be created. This option is only valid in combination with the -d (or --home) option. usermod will try to adapt the ownership of the files and to copy the modes, ACL and extended attributes, but manual changes might be needed afterwards. -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). Note: This option is not recommended because the password (or encrypted password) will be visible by users listing the processes. You should make sure the password respects the system´s password policy. -R, --root CHROOT_DIR Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory. -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 new numerical value of the user´s ID. This value must be unique, unless the -o option is used. The value must be non-negative. The user´s mailbox, and any files which the user owns and which are located in the user´s home directory will have the file user ID changed automatically. The ownership of files outside of the user´s home directory must be fixed manually. No checks will be performed with regard to the UID_MIN, UID_MAX, SYS_UID_MIN, or SYS_UID_MAX from /etc/login.defs. -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. Note: if you wish to unlock the account (not only access with a password), you should also set the EXPIRE_DATE (for example to 99999, or to the EXPIRE value from /etc/default/useradd). -Z, --selinux-user SEUSER The new SELinux user for the user´s login. A blank SEUSER will remove the SELinux user mapping for user LOGIN (if any).
- /etc/group : Group account information.
- /etc/gshadow : Secure group account information.
- /etc/login.defs : Shadow password suite configuration.
- /etc/passwd : User account information.
- /etc/shadow : Secure user account information
chfn(1), chsh(1), passwd(1), crypt(3), gpasswd(8), groupadd(8), groupdel(8), groupmod(8), login.defs(5), useradd(8), userdel(8)