chmod : to change permission

Go through the below image:

Suppose, you have a directory with some files. Open this directory into terminal and type "ls -l"

here, "cubic_resume.png" file's permissions are: rwx | rw- | rwx

• owner/user : rwx    i.e. read, write and execute permission
• group : rw-    i.e. read and write permission
• other/everyone : rwx    i.e. read, write and execute permission

chmod to change permission :

• chmod [OPTION] MODE[,MODE] Filename
• chmod [OPTION] OCTAL-MODE Filename

See the example below...

 To change read, write and execute permission through octal value

• owner/user : rwx    i.e. 4+2+1 = 7
• group : rwx    i.e. 4+2+1 = 7
• other/everyone : rwx    i.e. 4+2+1 = 7

To remove read/write/execute permission from all users through symbolic value

u : user

g : group

o : other

a : all

+ : adding

- : removing

= : assigning

a-x means removing execute permission from all

To add no permission for all through octal value

To add:

• read, write and execute permission to user/owner
• read and write permission to group
• read permission to other/everyone

u+rwx, g+rw, o+r means adding read, write and execute permission to user/owner; adding read and write permission to group; adding read permission to other

If you face any problems to understand, please feel free to comment.
Happy Learning!