Linux usermod 命令
Linux usermod命令用于修改用户账号的各种设置，在多群组权限的情况下，十分常用。
官方定义为：
usermod - modify a user account
语法
用法为：
1 | $ usermod [options] LOGIN |
常用的几个参数为：
-a追加用户组，通常与-G一起使用-c COMMENT修改用户帐号的备注文字-e YYYY-MM-DD修改帐号的有效期限。-g newgroup修改用户所属的群组。-G groups修改用户所属的附加群组。
修改备注名字
正常情况下在创建用户的时候，不太会指定全名，此时可以使用-c来补全备注。
1 | $ usermod -c "Full Name" user |
上面的命令将用户user的备注更改为Full Name。
指定账号有效期
可以通过-e参数来指定账号的有效期，特别是在知道用户用过一段时间后就不在使用，这种情况十分有效。
1 | $ usermod -e 2015-12-12 user |
上面的命令将用户user的有效期定义到2015年12月12日。
重新指定用户组
参数-g将把用户的默认属组更新。
1 | $ usermod -g newgroup user |
上面的命令为把user默认组更改为newgroup。正常情况下，用户将在创建的时候默认创建一个同名的群组。
新增用户组
这个指令用的是最多的，也就是把用户同时追加到其他组，如下所示：
1 | $ usermod -a -G group1 group2 group3 user |
含义为把用户user同时追加到用户组group1、group2和group3。
1 | # 添加用户user1到组group1里。 |
实例
更改登录目录
1 | usermod -d /home/hnlinux root |
改变用户的uid
1 |
-f<缓冲天数> 修改在密码过期后多少天即关闭该帐号。
- -l<帐号名称> 修改用户帐号名称。
- -L 锁定用户密码，使密码无效。
- -s
修改用户登入后所使用的shell。 - -u
修改用户ID。 - -U 解除密码锁定。
OPTIONS
The options which apply to the usermod command are:
-a, --append
Add the user to the supplementary group(s). Use only with the -G option.
-b, --badnames
Allow names that do not conform to standards.
-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.
-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.
-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.
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.
The password will be written in the local /etc/passwd or /etc/shadow file. This might differ from the password database configured in your PAM configuration.
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.
-P, --prefix PREFIX_DIR
Apply changes in the PREFIX_DIR directory and use the configuration files from the PREFIX_DIR directory. This option does not chroot and is intended for preparing a cross-compilation target. Some limitations: NIS and LDAP users/groups are not verified. PAM authentication is using the host files. No SELINUX support.
-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).
-v, --add-subuids FIRST-LAST
Add a range of subordinate uids to the user's account.
This option may be specified multiple times to add multiple ranges to a users account.
No checks will be performed with regard to SUB_UID_MIN, SUB_UID_MAX, or SUB_UID_COUNT from /etc/login.defs.
-V, --del-subuids FIRST-LAST
Remove a range of subordinate uids from the user's account.
This option may be specified multiple times to remove multiple ranges to a users account. When both --del-subuids and --add-subuids are specified, the
removal of all subordinate uid ranges happens before any subordinate uid range is added.
No checks will be performed with regard to SUB_UID_MIN, SUB_UID_MAX, or SUB_UID_COUNT from /etc/login.defs.
-w, --add-subgids FIRST-LAST
Add a range of subordinate gids to the user's account.
This option may be specified multiple times to add multiple ranges to a users account.
No checks will be performed with regard to SUB_GID_MIN, SUB_GID_MAX, or SUB_GID_COUNT from /etc/login.defs.
-W, --del-subgids FIRST-LAST
Remove a range of subordinate gids from the user's account.
This option may be specified multiple times to remove multiple ranges to a users account. When both --del-subgids and --add-subgids are specified, the
removal of all subordinate gid ranges happens before any subordinate gid range is added.
No checks will be performed with regard to SUB_GID_MIN, SUB_GID_MAX, or SUB_GID_COUNT from /etc/login.defs.
-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).
CAVEATS
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, the user’s
name, or the user’s home directory is being changed. usermod checks this on Linux. On other platforms it only uses utmp to check if the user is logged in.
You must change the owner of any crontab files or at jobs manually.
You must make any changes involving NIS on the NIS server.
CONFIGURATION
The following configuration variables in /etc/login.defs change the behavior of this tool:
LASTLOG_UID_MAX (number)
Highest user ID number for which the lastlog entries should be updated. As higher user IDs are usually tracked by remote user identity and
authentication services there is no need to create a huge sparse lastlog file for them.
No LASTLOG_UID_MAX option present in the configuration means that there is no user ID limit for writing lastlog entries.
MAIL_DIR (string)
The mail spool directory. This is needed to manipulate the mailbox when its corresponding user account is modified or deleted. If not specified, a
compile-time default is used.
MAIL_FILE (string)
Defines the location of the users mail spool files relatively to their home directory.
The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create, move, or delete the user's mail spool.
MAX_MEMBERS_PER_GROUP (number)
Maximum members per group entry. When the maximum is reached, a new group entry (line) is started in /etc/group (with the same name, same password, and
same GID).
The default value is 0, meaning that there are no limits in the number of members in a group.
This feature (split group) permits to limit the length of lines in the group file. This is useful to make sure that lines for NIS groups are not larger
than 1024 characters.
If you need to enforce such limit, you can use 25.
Note: split groups may not be supported by all tools (even in the Shadow toolsuite). You should not use this variable unless you really need it.
SUB_GID_MIN (number), SUB_GID_MAX (number), SUB_GID_COUNT (number)
If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate group IDs) allocate SUB_GID_COUNT unused group IDs
from the range SUB_GID_MIN to SUB_GID_MAX for each new user.
The default values for SUB_GID_MIN, SUB_GID_MAX, SUB_GID_COUNT are respectively 100000, 600100000 and 65536.
SUB_UID_MIN (number), SUB_UID_MAX (number), SUB_UID_COUNT (number)
If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate user IDs) allocate SUB_UID_COUNT unused user IDs
from the range SUB_UID_MIN to SUB_UID_MAX for each new user.
The default values for SUB_UID_MIN, SUB_UID_MAX, SUB_UID_COUNT are respectively 100000, 600100000 and 65536.
chfn(1), chsh(1), passwd(1), crypt(3), gpasswd(8), groupadd(8), groupdel(8), groupmod(8), login.defs(5), subgid(5), subuid(5), useradd(8), userdel(8).