CentOS User Account Management

CentOS User Account Management

1. User Management

/Etc/passwd user name configuration file

/Etc/shadow User Password Configuration File
(1) structure of/etc/passwd:
Username: password: uid: gid: commit: user home path: shell

Note:

Uid and gid are auto-incrementing by default;

User's home directory-common users in/home, root in/(or ~);

Shell refers to the logon method-Common/bin/bash,/sbin/nologin (set as not logged on );

(2) structure of/etc/shadow

Username: User Name

Password: password, encryption mode $1 (md5), $5 (SHA-256), $6 (sha-512 ),!! No Password, * locking users

Last password change time: the number of days from January 1

How many days can I change my password:

Password expiration time:

Warning password invalidation: Notification several days before password invalidation

Expiration date: change the password in time to prevent unavailability of users

Reserved fields

Plug: Linux time synchronization

Date-s defines the time (date Format)

Ntpdate time server address

Hwclock-h: Same as the time in BIOS

2. Operations on user accounts

(1) Basic operations

Add User: useradd-u [uid]-g [gid]-G [group]-d [home dir path]-M [don't create home path]

-S [shell such as/sbin/nologin,/bin/bash] [username] can create user-specified groups

Delete user: userdel-r is deleted along with the Home Directory

Add User Group: groupadd-g [gid] [groupname]

Delete user group: groupdel [groupname]

View: id [username]

Instance: the user fails to be switched and the user's home directory does not exist.

Solution:

# Mkdir

# Cp-rv/etc/skel/. B *

; # If you want to delete them together, the owner Group of the home directory must be the user

(2) Change the attributes of a user account

Usermod-u-g-G-s-d-L: Locked User-U: unlocked user

Chfn username: added a description of the user account

Set Password

Randomly generated password: mkpasswd-l fixed length-s defined special character-yum install-y mkpasswd)

Record tool: keepass

3. Switch users

Su-[username] Full switchover, environment variables and home directory switchover

Su-C ''command'-the user temporarily executes the command with the permission of a user

Sudo allows common users to temporarily execute commands with specified user permissions,

Set the User Password sudo/bin/ls/root/

Change the mongodo configuration, "user ALL = (source user) NOPASSWD :( no password required) the absolute path of the command to be executed"

Instance 1: Enter the password only once

Solution: passwd -- stdin

Echo-e "[new password] \ n [new passwd] \ n" | passwdpasswd -- stdin [username]; \ n is a carriage return-e Escape Character

Instance 2: remote login connection is too slow

Solution:

Vim/etc/ssh/sshd_config

Enable UseDNS * and change the value to no

/Etc/init. d/sshd restart or service sshd restart

Instance 3: disabling remote root does not prevent the use of root permissions to execute commands

Solution:

1. disable root Remote Login

Vim/etc/ssh/sshd_config

Enable PermitRootLogin .. and change the value to no.

/Etc/init. d/sshd restart or service sshd restart

2. Change the switch execution permission

Mongodo

[Username] ALL = (root) NOPASSWD:/bin/ls,/bin/su (location: root line) do not change the password

Su-[username]

Sudo su-