User Management¶

In this chapter you will learn how to manage users.

Objectives: In this chapter, future Linux administrators will learn how to:

add, delete or modify a group;
add, delete or modify a user;
understand the files associated with users and groups and learn how to manage them;
change the owner or the group owner of a file;
secure user accounts;
change identity.

users

Knowledge:
Complexity:

Reading time: 30 minutes

General¶

Each user must have a group, which is called the user's primary group.

Several users can be part of the same group.

Groups other than the primary group are called the user's supplementary groups.

Note

Each user has a primary group and can be invited into one or more supplementary groups.

Groups and users are managed by their unique numerical identifiers GID and UID.

UID: User IDentifier. Unique user ID.
GID: Group IDentifier. Unique group identifier.

Both UID and GID are recognized by the kernel, which means that the Super Admin is not necessarily the root user, as long as the uid=0 user is the Super Admin.

The files related to users/groups are:

/etc/passwd
/etc/shadow
/etc/group
/etc/gshadow
/etc/skel/
/etc/default/useradd
/etc/login.defs

Danger

You should always use the administration commands instead of manually editing the files.

Group management¶

Modified files, added lines:

/etc/group
/etc/gshadow

`groupadd` command¶

The groupadd command adds a group to the system.

groupadd [-f] [-g GID] group

Example:

$ sudo groupadd -g 1012 GroupeB

Option	Description
`-g GID`	`GID` of the group to create.
`-f`	The system chooses a `GID` if the one specified by the `-g` option already exists.
`-r`	Creates a system group with a `GID` between `SYS_GID_MIN` and `SYS_GID_MAX`. These two variables are defined in `/etc/login.defs`.

Group naming rules:

No accents or special characters;
Different from the name of an existing user or system files.

Note

Under Debian, the administrator should use, except in scripts intended to be portable to all Linux distributions, the addgroup and delgroup commands as specified in the man:

$ man addgroup
DESCRIPTION
adduser and addgroup add users and groups to the system according to command line options and configuration information
in /etc/adduser.conf. They are friendlier front ends to the low-level tools like useradd, groupadd and usermod programs,
by default, choosing Debian policy conformant UID and GID values, creating a home directory with skeletal configuration,
running a custom script, and other features.

Command `groupmod`¶

The groupmod command allows you to modify an existing group on the system.

groupmod [-g GID] [-n nom] group

Example:

$ sudo groupmod -g 1016 GroupP
$ sudo groupmod -n GroupC GroupB

Option	Description
`-g GID`	New `GID` of the group to modify.
`-n name`	New name.

It is possible to change the name of a group, its GID or both simultaneously.

After modification, the files belonging to the group have an unknown GID. They must be reassigned the new GID.

$ sudo find / -gid 1002 -exec chgrp 1016 {} \;

`groupdel` command¶

The groupdel command is used to delete an existing group on the system.

groupdel group

Example:

$ sudo groupdel GroupC

Tip

When deleting a group, there are two conditions that can occur:

If a user has a unique primary group and you issue the groupdel command on that group, you will be prompted that there is a specific user under the group and it cannot be deleted.
If a user belongs to a supplementary group (not the primary group for the user) and that group is not the primary group for another user on the system, then the groupdel command will delete the group without any additional prompts.

Examples:

Shell > useradd testa
Shell > id testa
uid=1000(testa) gid=1000(testa) group=1000(testa)
Shell > groupdel testa
groupdel: cannot remove the primary group of user 'testa'

Shell > groupadd -g 1001 testb
Shell > usermod -G testb root
Shell > id root
uid=0(root) gid=0(root) group=0(root),1001(testb)
Shell > groupdel testb

Tip

When you delete a user using the userdel -r command, the corresponding primary group is also deleted. The primary group name is usually the same as the username.

Tip

Each group has a unique GID. A group can be used by multiple users as a supplementary group. By convention, The GID of super administrator is 0. The GIDS reserved for some services or processes are 201~999, which are called system groups or pseudo user groups. The GID for users is usually greater than or equal to 1000. These are related to /etc/login.defs, which we will talk about later.

# Comment line ignored
shell > cat  /etc/login.defs
MAIL_DIR        /var/spool/mail
UMASK           022
HOME_MODE       0700
PASS_MAX_DAYS   99999
PASS_MIN_DAYS   0
PASS_MIN_LEN    5
PASS_WARN_AGE   7
UID_MIN                  1000
UID_MAX                 60000
SYS_UID_MIN               201
SYS_UID_MAX               999
GID_MIN                  1000
GID_MAX                 60000
SYS_GID_MIN               201
SYS_GID_MAX               999
CREATE_HOME     yes
USERGROUPS_ENAB yes
ENCRYPT_METHOD SHA512

Tip

Since a user is necessarily part of a group, it is best to create the groups before adding the users. Therefore, a group may not have any members.

`/etc/group` file¶

This file contains the group information (separated by :).

$ sudo tail -1 /etc/group
GroupP:x:516:patrick
  (1)  (2)(3)   (4)

1: Name of the group.
2: The group password is identified by x. The group password is stored in /etc/gshadow.
3: GID.
4: Supplementary users in the group (excluding the unique primary user).

Note

Each line in the /etc/group file corresponds to a group. The primary user info is stored in /etc/passwd.

`/etc/gshadow` file¶

This file contains the security information about the groups (separated by :).

$ sudo grep GroupA /etc/gshadow
GroupA:$6$2,9,v...SBn160:alain:rockstar
   (1)      (2)            (3)      (4)

1: Name of the group.
2: Encrypted password.
3: Name of the group administrator.
4: Supplementary users in the group (excluding the unique primary user).

Warning

The name of the group in /etc/group and /etc/gshadow must correspond one by one, that is, each line in the /etc/group file must have a corresponding line in the /etc/gshadow file.

An ! in the password indicates that it is locked. Thus, no user can use the password to access the group (since group members do not need it).

User management¶

Definition¶

A user is defined as follows in the /etc/passwd file:

1: Login name;
2: Password identification, x indicates that the user has a password, the encrypted password is stored in the second field of /etc/shadow;
3: UID;
4: GID of the primary group;
5: Comments;
6: Home directory;
7: Shell (/bin/bash, /bin/nologin, ...).

There are three types of users:

root(uid=0): the system administrator;
system users(uid is one of the 201~999): Used by the system to manage application access rights;
regular user(uid>=1000): Other account to log in to the system.

Modified files, added lines:

/etc/passwd
/etc/shadow

`useradd` command¶

The useradd command is used to add a user.

useradd [-u UID] [-g GID] [-d directory] [-s shell] login

Example:

$ sudo useradd -u 1000 -g 1013 -d /home/GroupC/carine carine

Option	Description
`-u UID`	`UID` of the user to create.
`-g GID`	`GID` of the primary group. The `GID` here can also be a `group name`.
`-G GID1,[GID2]...`	`GID` of the supplementary groups. The `GID` here can also be a `group name`. Multiple supplementary groups can be specified, separated by commas.
`-d directory`	Home directory.
`-s shell`	Shell.
`-c COMMENT`	Add a comment.
`-U`	Adds the user to a group with the same name created simultaneously. If this option is not written by default, a group with the same name will be created when the user is created.
`-M`	Do not create the user's home directory.
`-r`	Create a system account.

At creation, the account has no password and is locked.

A password must be assigned to unlock the account.

When the useradd command does not have any options, it appears:

Create a home directory with the same name;
Create a primary group with the same name;
The default shell is bash;
The user's uid and primary group gid are automatically recorded from 1000, and usually uid and gid are the same.

Shell > useradd test1

Shell > tail -n 1 /etc/passwd
test1:x:1000:1000::/home/test1:/bin/bash

Shell > tail -n 1 /etc/shadow
test1:!!:19253:0:99999:7:::

Shell > tail -n 1 /etc/group ; tail -n 1 /etc/gshadow
test1:x:1000:
test1:!::

Account naming rules:

No accents, capital letters or special characters;
Different from the name of an existing group or system file;
Optional: set the options -u, -g, -d and -s at creation.

Warning

The home directory tree must be created except for the last directory.

The last directory is created by the useradd command, which takes the opportunity to copy the files from /etc/skel into it.

A user can belong to several groups in addition to their primary group.

Example:

$ sudo useradd -u 1000 -g GroupA -G GroupP,GroupC albert

Note

Under Debian, you will have to specify the -m option to force the creation of the login directory or set the CREATE_HOME variable in the /etc/login.defs file. In all cases, the administrator should use the adduser and deluser commands as specified in the man, except in scripts intended to be portable to all Linux distributions:

$ man useradd
DESCRIPTION
    **useradd** is a low-level utility for adding users. On Debian, administrators should usually use **adduser(8)**
     instead.

Default value for user creation.¶

Modification of the file /etc/default/useradd.

useradd -D [-b directory] [-g group] [-s shell]

Example:

$ sudo useradd -D -g 1000 -b /home -s /bin/bash

Option	Description
`-D`	Sets the default values for user creation.
`-b directory`	Sets the default login directory.
`-g group`	Sets the default group.
`-s shell`	Sets the default shell.
`-f`	The number of days after the password expires before the account is disabled.
`-e`	The date the account will be disabled.

`usermod` command¶

The usermod command allows to modify a user.

usermod [-u UID] [-g GID] [-d directory] [-m] login

Example:

$ sudo usermod -u 1044 carine

Options identical to the useradd command.

Option	Description
`-m`	Associated with the `-d` option, moves the contents of the old login directory to the new one.If the old home directory does not exist, a new home directory will not be created; If the new home directory does not exist, it is created.
`-l login`	New login name. After you modify the login name, you also need to modify the name of the home directory to match it.
`-e YYYY-MM-DD`	Account expiration date.
`-L`	Permanently lock account. That is, an `!` is added at the beginning of the `/etc/shadow` password field
`-U`	Unlocks the account.
`-a`	Append the user's supplementary groups, which must be used together with the `-G` option.
`-G`	Modify the user's supplementary groups to overwrite the previous supplementary groups.

Tip

To be modified, a user must be disconnected and have no running processes.

After changing the identifier, the files belonging to the user have an unknown UID. It must be reassigned to the new UID.

Where 1000 is the old UID and 1044 is the new one. Examples are as follows:

$ sudo find / -uid 1000 -exec chown 1044: {} \;

Locking and unlocking of user account, Examples are as follows:

Shell > usermod -L test1
Shell > grep test1 /etc/shadow
test1:!$6$n.hxglA.X5r7X0ex$qCXeTx.kQVmqsPLeuvIQnNidnSHvFiD7bQTxU7PLUCmBOcPNd5meqX6AEKSQvCLtbkdNCn.re2ixYxOeGWVFI0:19259:0:99999:7:::

Shell > usermod -U test1

The difference between the -aG option and the -G option can be explained by the following example:

Shell > useradd test1
Shell > passwd test1
Shell > groupadd groupA ; groupadd groupB ; groupadd groupC ; groupadd groupD
Shell > id test1
uid=1000(test1) gid=1000(test1) groups=1000(test1)

Shell > gpasswd -a test1 groupA
Shell > id test1
uid=1000(test1) gid=1000(test1) groups=1000(test1),1002(groupA)

Shell > usermod -G groupB,groupC test1
Shell > id test1 
uid=1000(test1) gid=1000(test1) gorups=1000(test1),1003(groupB),1004(groupC)

Shell > usermod -aG groupD test1
uid=1000(test1) gid=1000(test1) groups=1000(test1),1003(groupB),1004(groupC),1005(groupD)

`userdel` command¶

The userdel command allows you to delete a user's account.

$ sudo userdel -r carine

Option	Description
`-r`	Delete the user's home directory and mail files located in the `/var/spool/mail/` directory

Tip

To be deleted, a user must be logged out and have no running processes.

The userdel command removes the corresponding lines in /etc/passwd, / etc/shadow, /etc/group, /etc/gshadow. As mentioned above, userdel -r will also delete the corresponding primary group of the user.

`/etc/passwd` file¶

This file contains user information (separated by :).

$ sudo head -1 /etc/passwd
root:x:0:0:root:/root:/bin/bash
(1)(2)(3)(4)(5)  (6)    (7)

1: Login name;
2: Password identification, x indicates that the user has a password, the encrypted password is stored in the second field of /etc/shadow;
3: UID;
4: GID of the primary group;
5: Comments;
6: Home directory;
7: Shell (/bin/bash, /bin/nologin, ...).

`/etc/shadow` file¶

This file contains the users' security information (separated by :).

$ sudo tail -1 /etc/shadow
root:$6$...:15399:0:99999:7:::
 (1)    (2)  (3) (4) (5) (6)(7,8,9)

1: Login name.
2: Encrypted password. Uses the SHA512 encryption algorithm, defined by the ENCRYPT_METHOD of /etc/login.defs.
3: The time when the password was last changed, the timestamp format, in days. The so-called timestamp is based on January 1, 1970 as the standard time. Every time one day goes by, the timestamp is +1.
4: Minimum lifetime of the password. That is, the time interval between two password changes (related to the third field), in days. Defined by the PASS_MIN_DAYS of /etc/login.defs, the default is 0, that is, when you change the password for the second time, there is no restriction. However, if it is 5, it means that it is not allowed to change the password within 5 days, and only after 5 days.
5: Maximum lifetime of the password. That is, the validity period of the password (related to the third field). Defined by the PASS_MAX_DAYS of /etc/login.defs.
6: The number of warning days before the password expires (related to the fifth field). The default is 7 days, defined by the PASS_WARN_AGE of /etc/login.defs.
7: Number of days of grace after password expiration (related to the fifth field).
8: Account expiration time, the timestamp format, in days. Note that an account expiration differs from a password expiration. In case of an account expiration, the user shall not be allowed to login. In case of a password expiration, the user is not allowed to login using her password.
9: Reserved for future use.

Danger

For each line in the /etc/passwd file there must be a corresponding line in the /etc/shadow file.

For time stamp and date conversion, please refer to the following command format:

# The timestamp is converted to a date, "17718" indicates the timestamp to be filled in.
Shell > date -d "1970-01-01 17718 days" 

# The date is converted to a timestamp, "2018-07-06" indicates the date to be filled in.
Shell > echo $(($(date --date="2018-07-06" +%s)/86400+1))

File owners¶

Danger

All files necessarily belong to one user and one group.

The primary group of the user creating the file is, by default, the group that owns the file.

Modification commands¶

`chown` command¶

The chown command allows you to change the owners of a file.

chown [-R] [-v] login[:group] file

Examples:

$ sudo chown root myfile
$ sudo chown albert:GroupA myfile

Option	Description
`-R`	Recursively changes the owners of the directory and all files under the directory.
`-v`	Displays the executed changes.

To change only the owner user:

$ sudo chown albert file

To modify only the owner group:

$ sudo chown :GroupA file

Changing the user and owner group:

$ sudo chown albert:GroupA file

In the following example the group assigned will be the primary group of the specified user.

$ sudo chown albert: file

Change the owner and group of all files in a directory

$ sudo chown -R albert:GroupA /dir1

`chgrp` command¶

The chgrp command allows you to change the owner group of a file.

chgrp [-R] [-v] group file

Example:

$ sudo chgrp group1 file

Option	Description
`-R`	Recursively changes the groups of the directory and all files under the directory.
`-v`	Displays the executed changes.

Note

It is possible to apply to a file an owner and an owner group by taking as reference those of another file:

chown [options] --reference=RRFILE FILE

For example:

chown --reference=/etc/groups /etc/passwd

Guest management¶

`gpasswd` command¶

The command gpasswd allows to manage a group.

gpasswd [option] group

Examples:

$ sudo gpasswd -A alain GroupA
[alain]$ gpasswd -a patrick GroupA

Option	Description
`-a USER`	Adds the user to the group. For the added user, this group is a supplementary group.
`-A USER,...`	Set the list of administrative users.
`-d USER`	Remove the user from the group.
`-M USER,...`	Set the list of group members.

The command gpasswd -M acts as a modification, not an addition.

# gpasswd GroupeA
New Password:
Re-enter new password:

Note

In addition to using gpasswd -a to add users to a group, you can also use the usermod -G or usermod -AG mentioned earlier.

`id` command¶

The id command displays the group names of a user.

id USER

Example:

$ sudo id alain
uid=1000(alain) gid=1000(GroupA) groupes=1000(GroupA),1016(GroupP)

`newgrp` command¶

The newgrp command can select a group from the user's supplementary groups as the user's new temporary primary group. The newgrp command every time you switch a user's primary group, there will be a new child shell（child process). Be careful! child shell and sub shell are different.

newgrp [secondarygroups]

Example:

Shell > useradd test1
Shell > passwd test1
Shell > groupadd groupA ; groupadd groupB 
Shell > usermod -G groupA,groupB test1
Shell > id test1
uid=1000(test1) gid=1000(test1) groups=1000(test1),1001(groupA),1002(groupB)
Shell > echo $SHLVL ; echo $BASH_SUBSHELL
1
0

Shell > su - test1
Shell > touch a.txt
Shell > ll
-rw-rw-r-- 1 test1 test1 0 10月  7 14:02 a.txt
Shell > echo $SHLVL ; echo $BASH_SUBSHELL
1
0

# Generate a new child shell
Shell > newgrp groupA
Shell > touch b.txt
Shell > ll
-rw-rw-r-- 1 test1 test1  0 10月  7 14:02 a.txt
-rw-r--r-- 1 test1 groupA 0 10月  7 14:02 b.txt
Shell > echo $SHLVL ; echo $BASH_SUBSHELL
2
0

# You can exit the child shell using the `exit` command
Shell > exit
Shell > logout
Shell > whoami
root

Securing¶

`passwd` command¶

The passwd command is used to manage a password.

passwd [-d] [-l] [-S] [-u] [login]

Examples:

Shell > passwd -l albert
Shell > passwd -n 60 -x 90 -w 80 -i 10 patrick

Option	Description
`-d`	Permanently removes the password. For root (uid=0) use only.
`-l`	Permanently lock user account. For root (uid=0) use only.
`-S`	Displays the account status. For root (uid=0) use only.
`-u`	Permanently unlocks user account. For root (uid=0) use only.
`-e`	Permanently expires the password. For root (uid=0) use only.
`-n DAYS`	Minimum password lifetime. Permanent change. For root (uid=0) use only.
`-x DAYS`	Maximum password lifetime. Permanent change. For root (uid=0) use only.
`-w DAYS`	Warning time before expiration. Permanent change. For root (uid=0) use only.
`-i DAYS`	Delay before deactivation when the password expires. Permanent change. For root (uid=0) use only.

Use password -l, that is, add "!!" at the beginning of the password field of the user corresponding to /etc/shadow.

Example:

Alain changes his password:

[alain]$ passwd

root changes Alain's password

$ sudo passwd alain

Note

The passwd command is available to users to change their password (the old password is requested). The administrator can change the passwords of all users without restriction.

They will have to comply with the security restrictions.

When managing user accounts by shell script, it may be useful to set a default password after creating the user.

This can be done by passing the password to the passwd command.

Example:

$ sudo echo "azerty,1" | passwd --stdin philippe

Warning

The password is entered in clear text, passwd takes care of encrypting it.

`chage` command¶

The chage command is change user password expiry information.

chage [-d date] [-E date] [-I days] [-l] [-m days] [-M days] [-W days] [login]

Example:

$ sudo chage -m 60 -M 90 -W 80 -I 10 alain

Option	Description
`-I DAYS`	Delay before deactivation, password expired. Permanent change.
`-l`	Displays the policy details.
`-m DAYS`	Minimum lifetime of the password. Permanent change.
`-M DAYS`	Maximum lifetime of the password. Permanent change.
`-d LAST_DAY`	Last password change. You can use the days' timestamp style or the YYYY-MM-DD style. Permanent change.
`-E EXPIRE_DATE`	Account expiration date. You can use the days' timestamp style or the YYYY-MM-DD style. Permanent change.
`-W WARN_DAYS`	Warning time before expiration. Permanent change.

Examples:

# The `chage` command also offers an interactive mode.
$ sudo chage philippe

# The `-d` option forces the password to be changed at login.
$ sudo chage -d 0 philippe

User account management with chage

Advanced management¶

Configuration files:

/etc/default/useradd
/etc/login.defs
/etc/skel

Note

Editing the /etc/default/useradd file is done with the useradd command.

The other files are to be modified with a text editor.

`/etc/default/useradd` file¶

This file contains the default data settings.

Tip

When creating a user, if the options are not specified, the system uses the default values defined in /etc/default/useradd.

This file is modified by the command useradd -D (useradd -D entered without any other option displays the contents of the /etc/default/useradd file).

Shell > grep -v ^# /etc/default/useradd 
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes

Parameters	Comment
`GROUP`	Default primary group GID.
`HOME`	Define the directory path of the upper level of the common user's home directory.
`INACTIVE`	Number of days of grace after password expiration. Corresponds to the 7th field of the `/etc/shadow` file. `-1` value means that the grace period feature is turned off.
`EXPIRE`	Account expiration date. Corresponds to the 8th field of the `/etc/shadow` file.
`SHELL`	Command interpreter.
`SKEL`	Skeleton directory of the login directory.
`CREATE_MAIL_SPOOL`	Mailbox creation in `/var/spool/mail/`.

If you do not need a primary group with the same name when creating users, you can do this:

Shell > useradd -N test2
Shell > id test2
uid=1001(test2) gid=100(users) groups=100(users)

`/etc/login.defs` file¶

# Comment line ignored
shell > cat  /etc/login.defs
MAIL_DIR        /var/spool/mail
UMASK           022
HOME_MODE       0700
PASS_MAX_DAYS   99999
PASS_MIN_DAYS   0
PASS_MIN_LEN    5
PASS_WARN_AGE   7
UID_MIN                  1000
UID_MAX                 60000
SYS_UID_MIN               201
SYS_UID_MAX               999
GID_MIN                  1000
GID_MAX                 60000
SYS_GID_MIN               201
SYS_GID_MAX               999
CREATE_HOME     yes
USERGROUPS_ENAB yes
ENCRYPT_METHOD SHA512

UMASK 022: This means that the permission to create a file is 755 (rwxr-xr-x). However, for the sake of security, GNU/Linux does not have x permission for newly created files, this restriction applies to root(uid=0) and ordinary users(uid>=1000). For example:

Shell > touch a.txt
Shell > ll
-rw-r--r-- 1 root root     0 Oct  8 13:00 a.txt

HOME_MODE 0700: The permissions of an ordinary user's home directory. Does not work for root's home directory.

Shell > ll -d /root
dr-xr-x---. 10 root root 4096 Oct  8 13:12 /root

Shell > ls -ld /home/test1/
drwx------ 2 test1 test1 4096 Oct  8 13:10 /home/test1/

USERGROUPS_ENAB yes: "When you delete a user using the userdel -r command, the corresponding primary group is also deleted." Why? That's the reason.

`/etc/skel` directory¶

When a user is created, their home directory and environment files are created. You can think of the files in the /etc/skel/ directory as the file templates you need to create users.

These files are automatically copied from the /etc/skel directory.

.bash_logout
.bash_profile
.bashrc

All files and directories placed in this directory will be copied to the user tree when they are created.

Identity change¶

`su` command¶

The su command allows you to change the identity of the connected user.

su [-] [-c command] [login]

Examples:

$ sudo su - alain
[albert]$ su - root -c "passwd alain"

Option	Description
`-`	Loads the user's complete environment.
`-c` command	Executes the command under the user's identity.

If the login is not specified, it will be root.

Standard users will have to type the password for the new identity.

Tip

You can use the exit/logout command to exit users who have been switched. It should be noted that after switching users, there is no new child shell or sub shell, for example:

Shell > whoami
root
Shell > echo $SHLVL ; echo $BASH_SUBSHELL
1
0

Shell > su - test1
Shell > echo $SHLVL ; echo $BASH_SUBSHELL
1
0

Attention please! su and su - are different, as shown in the following example:

Shell > whoami
test1
Shell > su root
Shell > pwd
/home/test1

Shell > env
...
USER=test1
PWD=/home/test1
HOME=/root
MAIL=/var/spool/mail/test1
LOGNAME=test1
...

Shell > whoami
test1
Shell > su - root
Shell > pwd
/root

Shell > env
...
USER=root
PWD=/root
HOME=/root
MAIL=/var/spool/mail/root
LOGNAME=root
...

So, when you want to switch users, remember not to lose the -. Because the necessary environment variable files are not loaded, there may be problems running some programs.

Última actualización: 20 de noviembre de 2022

User Management¶

General¶

Group management¶

groupadd command¶

Command groupmod¶

groupdel command¶

/etc/group file¶

/etc/gshadow file¶

User management¶

Definition¶

useradd command¶

Default value for user creation.¶

usermod command¶

userdel command¶

/etc/passwd file¶

/etc/shadow file¶

File owners¶

Modification commands¶

chown command¶

chgrp command¶

Guest management¶

gpasswd command¶

id command¶

newgrp command¶

Securing¶

passwd command¶

chage command¶

Advanced management¶

/etc/default/useradd file¶

/etc/login.defs file¶

/etc/skel directory¶

Identity change¶

su command¶

`groupadd` command¶

Command `groupmod`¶

`groupdel` command¶

`/etc/group` file¶

`/etc/gshadow` file¶

`useradd` command¶

`usermod` command¶

`userdel` command¶

`/etc/passwd` file¶

`/etc/shadow` file¶

`chown` command¶

`chgrp` command¶

`gpasswd` command¶

`id` command¶

`newgrp` command¶

`passwd` command¶

`chage` command¶

`/etc/default/useradd` file¶

`/etc/login.defs` file¶

`/etc/skel` directory¶

`su` command¶