Detailed explanation of permission management commands in Linux (chmod/chown/chgrp/unmask)

chmod [{ugoa}{+-=}{rwx}] [file or directory] 
chmod [mode=421] [file or directory]
 -R recursive modification # The first modification method chmod [{ugoa}{+-=}{rwx}] [file or directory]
ugoa:
 u: Owner g: Group o: Others a: Everyone +-=:
 +: Add a permission to a file or directory -: Reduce a permission to a file or directory =: Give a file or directory new permissions, based on the current permissions # The second modification method chmod [mode=421] [file or directory]
rwx:
 r:4
 w:2
 x:1
rwxrw-r--
 Permission: 764 (4+2+1=7/4+2=6/4)

# The first way to increase permissions chmod g+x test.txt
 
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -l test.txt
-rw-r--r-- 1 root root 11 Nov 28 15:39 test.txt
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# chmod g+x test.txt
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -l test.txt
-rw-r-xr-- 1 root root 11 Nov 28 15:39 test.txt

# The second way to increase permissions: chmod 777 test.txt

[root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -l test.txt
-rw-r-xr-- 1 root root 11 Nov 28 15:39 test.txt
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# chmod 777 test.txt
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -l test.txt
-rwxrwxrwx 1 root root 11 Nov 28 15:39 test.txt

# Create a new folder test under /tmp
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# mkdir test

# Create a new test.txt in the /tmp/test folder
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# touch test/test.txt

# View the files under the test file [root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -l test
total 0
-rw-r--r-- 1 root root 0 Nov 28 17:54 test.txt

# Check the permissions of the /tmp/test folder [root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -ld test
drwxr-xr-x 2 root root 4096 Nov 28 17:54 test

# Grant full permissions to the /tmp/test folder [root@izm5e2q95pbpe1hh0kkwoiz tmp]# chmod 777 test
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -ld test
drwxrwxrwx 2 root root 4096 Nov 28 17:54 test

[root@izm5e2q95pbpe1hh0kkwoiz tmp]# ls -l test/test.txt
-rw-r--r-- 1 root root 0 Nov 28 17:54 test/test.txt

# Add a new ordinary user and change the password [root@izm5e2q95pbpe1hh0kkwoiz tmp]# useradd eternity
[root@izm5e2q95pbpe1hh0kkwoiz tmp]# passwd eternity

# Use the eternity account and password 123456 to log in to the server # View the current directory [eternity@izm5e2q95pbpe1hh0kkwoiz ~]$ pwd
/home/eternity

# Enter the /tmp directory [eternity@izm5e2q95pbpe1hh0kkwoiz ~]$ cd /tmp

# Check the permissions of the /tmp/test directory, which has all permissions [eternity@izm5e2q95pbpe1hh0kkwoiz tmp]$ ls -ld test
drwxrwxrwx 2 root root 4096 Nov 28 17:54 test

# test.txt exists in the /tmp/test directory and has read permission [eternity@izm5e2q95pbpe1hh0kkwoiz tmp]$ ls -l test/test.txt
-rw-r--r-- 1 root root 0 Nov 28 17:54 test/test.txt

# Delete the test.txt file under /tmp/test [eternity@izm5e2q95pbpe1hh0kkwoiz tmp]$ rm test/test.txt
rm: remove write-protected regular empty file 'test/test.txt'? y

# Deletion is successful. At this time, test.txt no longer exists in the /tmp/test directory [eternity@izm5e2q95pbpe1hh0kkwoiz tmp]$ ls -l test/test.txt
ls: cannot access test/test.txt: No such file or directory

# Change the file owner (change the owner of test.txt from eternity to root)
chown root /tmp/test/test.txt

[root@izm5e2q95pbpe1hh0kkwoiz ~]# pwd
/root
[root@izm5e2q95pbpe1hh0kkwoiz ~]# ls -l /tmp/test/test.txt
-rw-r--r-- 1 eternity eternity 7 Nov 28 18:15 /tmp/test/test.txt
[root@izm5e2q95pbpe1hh0kkwoiz ~]# chown root /tmp/test/test.txt
[root@izm5e2q95pbpe1hh0kkwoiz ~]# ls -l /tmp/test/test.txt
-rw-r--r-- 1 root eternity 7 Nov 28 18:15 /tmp/test/test.txt

Command name: chgrp
The original meaning of the command in English: change file group ownership
Command path:/bin/chgrp
Execution permission: All users Function description: Change the group to which a file or directory belongs

# Change the group to which the file belongs (change the group to which test.txt belongs from eternity to eternityz)
chgrp eternityz /tmp/test/test.txt

# Current directory [root@izm5e2q95pbpe1hh0kkwoiz ~]# pwd
/root
# View detailed information [root@izm5e2q95pbpe1hh0kkwoiz ~]# ls -l /tmp/test/test.txt
-rw-r--r-- 1 root eternity 7 Nov 28 18:15 /tmp/test/test.txt
# Add eternityz group [root@izm5e2q95pbpe1hh0kkwoiz ~]# groupadd eternityz
# Change the group [root@izm5e2q95pbpe1hh0kkwoiz ~]# chgrp eternityz /tmp/test/test.txt
[root@izm5e2q95pbpe1hh0kkwoiz ~]# ls -l /tmp/test/test.txt
-rw-r--r-- 1 root eternityz 7 Nov 28 18:15 /tmp/test/test.txt

# View the default permissions of the file umask -S

# Check umask
umask

[root@izm5e2q95pbpe1hh0kkwoiz ~]# umask
0022

0022 in 0 Special permissions 022 ----w--w-

# Perform an XOR operation on all permissions 777 and 022 to get the default permission 777 rwx rwx rwx
022 --- -w- -w-
================
Directory rwx rx rx
File rwx r-- r--


# Change the umask value to change the default permission umask 077

# After changing the umask value, the default permissions become 777 rwx rwx rwx
077 --- rwx rwx
================
Directory rwx --- ---
File rw- --- ---

# The following experiment complies with the setting of changing the default permissions [root@izm5e2q95pbpe1hh0kkwoiz ~]# umask 077
[root@izm5e2q95pbpe1hh0kkwoiz ~]# mkdir /tmp/lyf
[root@izm5e2q95pbpe1hh0kkwoiz ~]# ls -ld /tmp/lyf
drwx------ 2 root root 4096 Nov 29 10:55 /tmp/lyf
[root@izm5e2q95pbpe1hh0kkwoiz ~]# touch /tmp/lyf/lyf
[root@izm5e2q95pbpe1hh0kkwoiz ~]# ls -l /tmp/lyf/lyf
-rw------ 1 root root 0 Nov 29 10:56 /tmp/lyf/lyf