Linux: user & group management

• userldel – delete user, delete user home directory (user -r)
• chage / passwd – managing password aging
  • chage -l user10  – lists password aging attributes for user
    • # chage -l user10
      Last password change : May 24, 2021
      Password expires : never
      Password inactive : never
      Account expires : never
      Minimum number of days between password change : 0
      Maximum number of days between password change : 99999
      Number of days of warning before password expires : 7
  • chage -E 2024-12-31 user10  – deactivate user user10 at 2024-12-31
  • chage -d 0 user60 – force to change the password at next login (аналог sudo passwd -e weril)
  • passwd -n 7 -x 15 -w 3 user5 – configures password aging for user5 with mindays (–n) set to 7, maxdays (–x) to 16, and warndays (–w) to 3 using the passwd
  • The chage command changes the number of days between password changes and the date of the last password change. This information is used by the system to determine when a user must change
    his/her password.
• gpasswd – define group administrator(s) & members, group password, disable access to group with newgrp
  • If a password is set the members can still use newgrp(1) without a password, and non-members must supply the password. Group passwords are an inherent security problem since more than one person is permitted to know the password. However, groups are a useful tool for permitting co-operation between different users.
• vipw / vigr – edit the password/group/shadow-password/shadow-group files
  • The vipw and vigr commands edits the files /etc/passwd and /etc/group, respectively. With the -s flag, they will edit the shadow versions of those files, /etc/shadow and /etc/gshadow, respectively. The programs will set the appropriate locks to prevent file corruption. When looking for an editor, the programs will first try the environment variable $VISUAL, then the environment variable $EDITOR, and finally the default editor, vi(1).
• pwck / grpck – verify integrity of password/group files
  • The pwck command verifies the integrity of the users and authentication information. It checks that all entries in /etc/passwd and /etc/shadow have the proper format and contain valid
    data. The user is prompted to delete entries that are improperly formatted or which have other uncorrectable errors.
• These four programs all operate on the normal and shadow password and group files: /etc/passwd, /etc/group, /etc/shadow, and /etc/gshadow.
  • pwconv – creates shadow from passwd and an optionally existing shadow
  • pwunconv – creates passwd from passwd and shadow and then removes shadow.
  • grpconv – creates gshadow from group and an optionally existing gshadow.
  • grpunconv – creates group from group and gshadow and then removes gshadow.

ID

root@serv:~# id
uid=0(root) gid=0(root) groups=0(root)

user@serv:~$ id
uid=1000(user) gid=1000(user) groups=1000(user),24(cdrom),25(floppy),29(audio),30(dip),44(video),46(plugdev),109(netdev)

user

sudo useradd -m -s /bin/bash weril
sudo passwd weril
sudo login weril - тестово логинемся
sudo passwd -e weril - (expire) делаем пароль протухшим (после авторизации пользователя заставят поменять пароль)
# sudo passwd -l weril - (lock) блокируем пользователя
sudo vi /etc/ssh/sshd_config - добавляем в AllowUsers в sshd (AllowUsers <username>@*)
sudo /etc/init.d/sshd restart - рестартуем службу (sudo service sshd restart)

При смене пароля может запрашивать старый пароль, мы его можем не знать (напр. потерял пользователь/учетная запись создана облаком), в таком случае меняем из под root.

sudo su
passwd weril

Добавление конкретного пользователя в sudo (sudoers).

sudo vi /etc/sudoers

## Allow root to run any commands anywhere
root ALL=(ALL) ALL
weril ALL=(ALL) ALL

В Centos чтобы не добавлять каждого пользователя отдельно есть группа wheel, в Ubuntu группа sudo. Если добавить в эту группу – будут так же права sudo.

sudo usermod -a -G wheel [user name]
sudo usermod -a -G sudo [user name]

groups

Просмотр групп без ID (с ID смотрим по ID).

$ groups
user cdrom floppy audio dip video plugdev netdev

Add group shared with GID 9999. В файле /etc/group хранятся все группы (бекап в /etc/group-). groupmod используется для модификации существующей группы.

$ sudo groupadd -g 9999 shared
$ tail -1 /etc/group
shared:x:9999:

$ sudo usermod -G shared test_user1
$ sudo usermod -G shared test_user2
$ tail -1 /etc/group
shared:x:9999:test_user1,test_user2 # shared - имя группы, х - пароль зашифрован (чаще всего отсутствует и хранится в отдельном файле), 9999 - id группы, test_user1/2 - члены группы