User, group, and permission-related directives in Linux

Users, Groups, permissions

Permissions: R, W, X

File:

• R: Readable, you can use similar commands such as cat to view the contents of the file;
• W: writable, can edit or delete this file;
• X: Executable, exacutable, can be at the command prompt as a command to submit to the kernel to run;

Directory:

• R: You can perform LS on this directory to list all internal files;
• W: Files can be created in this directory;
• X: You can switch to this directory using a CD, or you can use Ls-l to view the details of the internal files;

Rwx

• r--: Read-only
• R-x: Read and Execute
• ---: No permissions
• 0---: No permissions
• 1 001--x: Execution
• 2 010-w-: Write
• 3 011-wx: Write and Execute
• 4 r--: Read-only
• 5 101 R-x: Read and Execute
• 6 rw-: Read and Write
• 7 111 rwx: Read and write execution

User: UID,/etc/passwd

Group: GID,/etc/group

Shadow Password:

Users:/etc/shadow

Group:/etc/gshadow

User Category:

• Admin: 0
• Normal Users: 1-65535
  • System users: 1-499
  • General Users: 500-60000

User Group Category:

• Administrators group:
• Normal Group:
  • System Group:
  • General Group:

User Group Category:

• Private group: When a user is created, a group with the same name as the user name is automatically created if the group to which it belongs is not specified
• Basic group: Default group for users
• Additional groups, additional groups: groups other than the default group

/etc/passwd

• Account: Login Name
• Password: password
• Uid:
• GID: Basic Group ID
• Comment: Notes
• Home dir: Home directory
• Shell: User's default shell

/etc/shadow

• Account: Login Name
• Encrypted Password: encrypted password

Useradd USERNAME Groupadd GRPNAME

User management: Useradd, Userdel, Usermod, passwd, Chsh, CHFN, finger, id, chage

Group management: Groupadd, Groupdel, Groupmod, gpasswd

Rights Management: Chown, CHGRP, chmod, umask

/ETC/PASSWD: Username: Password: uid:gid: Comments: Home directory: Default Shell

/etc/group: Group name: Password: GID: List of users with this group attached to the group

/etc/shadow: User name: Password: The last time to change password: Minimum age: Maximum Age: Warning Time: Inactive time: Expiry time:

User management: Useradd, Userdel, Usermod, passwd, Chsh, CHFN, finger, id, chage

useradd [Options] USERNAME

• -U UID
• -G GID (Basic Group)
• -G GID,... (Additional groups)
• -C "COMMENT"
• -d/path/to/directory
• -S SHELL
• -m-k
• -M
• -r: Add System User/etc/login.defs

Userdel:userdel [option] USERNAME

-r: Delete User's home directory at the same time

ID: View user's account attribute information

• -U
• -G
• -G
• -N

Finger: View user account information finger USERNAME

Modify user account properties: Usermod

• -U UID
• -G GID
• -A
• -G GID: Does not use the-a option to overwrite previous additional groups;
• -C
• -d-m:
• -S
• -L
• -L: Lock account
• -U: Unlock Account

CHSH: Modifying the user's default shell

CHFN: Modifying annotation information

Password management: passwd [USERNAME]

• --stdin
• -L
• -U
• -D: Remove user password

PWCK: Checking user account Integrity

Group Management:

Create Group: Groupadd

Groupadd

• -G GID
• -R: Added as System group

Groupmod

• -G GID
• -N GRPNAME

Groupdel

GPASSWD: Setting a password for a group

Rights Management: R:w: x:

Three types of users: U: belong to the main G: Group O: Other users

Chown: Change file owner (only administrators can use this command)

# chown USERNAME File,...

• -R: Modify the owner of the directory and its internal files
• --reference=/path/to/somefile file,...

Chown username:grpname File,...

Chown USERNAME. GRPNAME file,...

# chgrp GRPNAME file,...-R

--reference=/path/to/somefile file,...

chmod: Modify permissions for a file

Modify permissions for three categories of users:

chmod MODE File,...

• -R
• --reference=/path/to/somefile file,...

To modify a user or some class of user rights: U,g,o,a

chmod user category =mode file,...

Modify some or some bit permissions for a certain class of users: U,g,o,a

chmod user category +|-mode file,...

User, group, and permission-related directives in Linux