1. Involved commands
adduser 用户名
useradd 选项 用户名
usermod 选项 用户名
userdel 选项 用户名
passwd 选项 用户名
groupadd 选项 用户组
groupmod 选项 用户组
groupdel 选项 用户组
2. User account management
2.1 Create a new user account
Note that it is best to use adduser to create a new user. Using useradd, ordinary users will not automatically create a home directory. When the user logs in for the first time, although the user can log in, an error will be reported: Could not chdir
to home directory /home/xxx: No such file or directory
/usr/bin/xauth: error in locking authority file /home/xxx/.Xauthority
and many commands cannot be used, such as ll
Recommended action summary
addgroup groupname1 #作为主组
addgroup groupname2 #作为从组
adduser username #默认操作，主组是username，shell是/bin/bash
usermod -s /bin/bash -g groupname1 -G groupname2 username
2.1.1 adduser
adduser helpdocs
adduser [--home DIR] [--shell SHELL] [--no-create-home] [--uid ID]
[--firstuid ID] [--lastuid ID] [--gecos GECOS] [--ingroup GROUP | --gid ID]
[--disabled-password] [--disabled-login] [--add_extra_groups]
[--encrypt-home] USER
Add a normal user
adduser --system [--home DIR] [--shell SHELL] [--no-create-home] [--uid ID]
[--gecos GECOS] [--group | --ingroup GROUP | --gid ID] [--disabled-password]
[--disabled-login] [--add_extra_groups] USER
Add a system user
adduser --group [--gid ID] GROUP
addgroup [--gid ID] GROUP
Add a user group
addgroup --system [--gid ID] GROUP
Add a system group
adduser USER GROUP
Add an existing user to an existing group
general options:
--quiet | -q don't give process information to stdout
--force-badname allow usernames which do not match the
NAME_REGEX[_SYSTEM] configuration variable
--extrausers uses extra users as the database
--help | -h usage message
--version | -v version number and copyright
--conf | -c FILE use FILE as configuration file
create user
adduser username1
The result is as shown below. You need to enter the password and enter it again to confirm. You can enter without filling in the following Full Name and Room Number. Enter is the default value. It is best to enter y to confirm.
Add an existing user to an existing group
Note: Here, groupname is the slave group of username1
adduser username1 groupname
2.1.2 useradd
useradd help documentation
Usage: useradd [options] LOGIN
useradd -D
useradd -D [options]
Options:
--badnames do not check for bad names
-b, --base-dir BASE_DIR base directory for the home directory of the
new account
--btrfs-subvolume-home use BTRFS subvolume for home directory
-c, --comment COMMENT GECOS field of the new account
-d, --home-dir HOME_DIR home directory of the new account
-D, --defaults print or change default useradd configuration
-e, --expiredate EXPIRE_DATE expiration date of the new account
-f, --inactive INACTIVE password inactivity period of the new account
-g, --gid GROUP name or ID of the primary group of the new
account
-G, --groups GROUPS list of supplementary groups of the new
account
-h, --help display this help message and exit
-k, --skel SKEL_DIR use this alternative skeleton directory
-K, --key KEY=VALUE override /etc/login.defs defaults
-l, --no-log-init do not add the user to the lastlog and
faillog databases
-m, --create-home create the user's home directory
-M, --no-create-home do not create the user's home directory
-N, --no-user-group do not create a group with the same name as
the user
-o, --non-unique allow to create users with duplicate
(non-unique) UID
-p, --password PASSWORD encrypted password of the new account
-r, --system create a system account
-R, --root CHROOT_DIR directory to chroot into
-P, --prefix PREFIX_DIR prefix directory where are located the /etc/* files
-s, --shell SHELL login shell of the new account
-u, --uid UID user ID of the new account
-U, --user-group create a group with the same name as the user
-Z, --selinux-user SEUSER use a specific SEUSER for the SELinux user mapping
--extrausers Use the extra users database
The simplest, create a new user according to the default operation
useradd username1
Set the new user's home directory. The default directory is /home/username
useradd -d /home/username1 username1
Set the shell for new users to log in. Shell means shell, which is the shell of the Linux system kernel. The default shell for users is /bin/sh. Bash is an enhanced version of sh, and sh is a reduced version of bash. For specific differences, please refer to: sh and bash
useradd -s /bin/bash username1
Set up a new user group, provided that username1 has not been created before. The default grouping is the username itself
useradd -g groupname1 -G groupname2,groupname3 username1
2.2 View user and user group information
2.2.1 View the groups to which the current user belongs
The first one is the current group, the others are optional groups to which they belong.
groups
2.2.1 View all groups
cat /etc/group
2.2.1 View all users
cat /etc/passwd
/etc/passwd is a text file that contains information for each user necessary to log in to the Linux system. It saves the user's useful information and
contains 7 fields: user name, password, user ID, group ID, user ID information, user's home directory and Shell.
Username (magesh): The username of the created user, with a length of 1 to 12 characters.
Password (x): The encrypted password is stored in the `/etc/shadow file.
User ID (506): represents the ID number of the user, and each user must have a unique ID. UID number 0 is reserved for the root user, UID numbers 1 to 99 are reserved for system users, and UID numbers 100-999 are reserved for system accounts and groups.
Group ID (507): It represents the ID number of the group. Each group must have a unique GID, which is stored in the /etc/group file.
User information (2g Admin - Magesh M): Represents the description field, which can be used to describe the user's information (LCTT Annotation: The original text here is suspicious).
Home directory (/home/mageshm): represents the user's home directory.
Shell (/bin/bash): represents the shell type used by the user.
2.3 Modify user account
usermod help documentation
Usage: usermod [options] LOGIN
Options:
-b, --badnames allow bad names
-c, --comment COMMENT new value of the GECOS field
-d, --home HOME_DIR new home directory for the user account
-e, --expiredate EXPIRE_DATE set account expiration date to EXPIRE_DATE
-f, --inactive INACTIVE set password inactive after expiration
to INACTIVE
-g, --gid GROUP force use GROUP as new primary group
-G, --groups GROUPS new list of supplementary GROUPS
-a, --append append the user to the supplemental GROUPS
mentioned by the -G option without removing
the user from other groups
-h, --help display this help message and exit
-l, --login NEW_LOGIN new value of the login name
-L, --lock lock the user account
-m, --move-home move contents of the home directory to the
new location (use only with -d)
-o, --non-unique allow using duplicate (non-unique) UID
-p, --password PASSWORD use encrypted password for the new password
-R, --root CHROOT_DIR directory to chroot into
-P, --prefix PREFIX_DIR prefix directory where are located the /etc/* files
-s, --shell SHELL new login shell for the user account
-u, --uid UID new UID for the user account
-U, --unlock unlock the user account
-v, --add-subuids FIRST-LAST add range of subordinate uids
-V, --del-subuids FIRST-LAST remove range of subordinate uids
-w, --add-subgids FIRST-LAST add range of subordinate gids
-W, --del-subgids FIRST-LAST remove range of subordinate gids
-Z, --selinux-user SEUSER new SELinux user mapping for the user account
2.3.1 Modify user groups
usermod -g groupname1 -G groupname2,groupname3 username1
2.3.2 Modify user name and account name
usermod -l newusrname username1
2.3.3 Modify user password
修改自己账号密码
passwd
修改别人账号密码，需要sudo或者root
sudo passwd username
2.3.4 Modify user home directory
usermod -d /newhomepath username1
2.4 User groups
2.4.1 Create user group
addgroup groupname
或者
adduser --group groupname
或者
groupadd groupname1
2.4.2 Delete user group
groupdel groupname1
2.4.3 User group switching
If a user belongs to multiple user groups at the same time, the user can switch between user groups to have the permissions of other user groups.
After logging in, the user can use the command newgrp to switch to another user group. The parameter of this command is the destination user group. For example:
newgrp groupname2
This command switches the current user to the groupname2 user group, provided that the groupname2 user group is indeed the user's primary group or additional group.