Linux User and Group management

return value of program output

Standard output return value: 0

Standard error Output return value: 1-255

echo $? To get the return value

/dev/null: Device data (data black hole)

Can output useless information to/dev/null such as Ls/var &>/dev/null

Set-c: Prompt the user before overwriting

Users & Groups: Core elements to achieve resource allocation

Groups: Containers for users and permissions, easy to manage users with the same permissions

Categories of users:

Admin Administrator ID is 0

System User 1-499 is non-interactive, deamon, similar to the service in win.

Users 500 after normal user

--UserID (numeric) /etc/passwd/storing user information

/etc/shadow: Store password

/etc/group

Password for the/etc/gshadow group

Resolution of name resolution user name and user ID

Group ID with User ID

Management Group 0

System Group 1-499

General user Group

3A Certification:

Authenticatioin: Password Vault

Authorization: Through the genus Master Group to achieve

Audit, through the operation log to achieve

Permissions: All Documents

File:

R

W

X:excute, the permissions that are submitted to the kernel to run,

Directory:

R: Can LS

W: Create or delete

X: You can CD to the directory, or LS to display the directory metadata information

Ls-la nine-bit permissions, owner, group, three other users

Permission matching mode when a user accesses a file: (mode)

1, whether the owner of the process is running in accordance with the owner of the file, is the main permission to run, otherwise enter the STEP2,

2, check whether the group is consistent, otherwise enter the STEP3

3, execute AS other user

Password file:

/etc/shadow

The format needs to know 7 fields separated by a colon

Account:passwd:UID:GID (Basic Group): GECOS (optional,comments):

Directory (home directory): Shell (user's default shell)/etc/shells

Group to which the user belongs:

Basic Group;

Additional groups (additional groups)

Useradd

Useradd USER1

Ls-l ' which useradd ' which adduser

If a base group is not specified when it is created, a group with the same name as the user is created as its base group. (Private Group)

Options

-u:uid Specify User ID useradd-u 888 USERNAME

-g:gid Specify basic group Useradd-g Testgroup or 888 USER

-G: Specify additional groups

-c:comment, add comment information

-D: Home directory, if this directory exists beforehand, there will be warning, copy/etc/skel (skeleton)

Useradd-d/tmp/test/user

-S: Specifies one of the shells,/etc/shells, using the absolute path

Useradd-s/bin/tcsh USER echo $SHELL view

-M: Do not specify user home directory

-r: Create system User (not logged in user, so no home directory)

Groupadd:

Three colon-delimited 4 fields/etc/group

GROUPNAME:PASSWD (dot character x): Gid:user_list (seperated by comma as an additional group)

Option

-g:gid

-R: System Group

Groupdel

Userdel

Linux User and Group management