chmod and chown are among those popular linux commands.

chmod : To modify access to files and folders by providing read/write/execute permissions.
chown : To change the ownership of a file or folder.

chmod

There are two ways in which the permissions can be changed/set.

The symbolic method is the one where we mention:

  1. Whose access to change/set (u [user], g [group], o [others], a [all])
  2. What kind of change in permissions (+ [add], [remove], = [set exactly])
  3. Which Permission (r [read], w [write], x [execute])

Example :
To remove read and write permission from group and other of file “myfile.txt”

chmod og-rw myfile.txt

To add execute permission to group of the file “myfile2.txt”

chmod g+x myfile2.txt

The numeric method (my personal favorite) adds up the numbers to determine what kind of permission a file should have:

4 = read
2 = write
1 = execute

Now here’s the magic:

1 = execute (1)
2 = write (2)
3 = write (2) +  execute (1)4 = read (4)
5 = read (4) + execute (1)
6 = read (4) + write (2)
7 = read (4) + write (2) + execute (1)

And the only extra thing to remember is the sequence of permission, it’s always
User -> Group -> Others

Example:
To set the permission for a file “myfile2.txt” such as:
a. User has full (read, write and execute) permission … (read+write+execute = 4+2+1 = 7)
b. Group has read and write permission … (read+write = 4+2 = 6)
c. Others have only read permission … (read = 4)

chmod 764 myfile2.txt

Note : 777 is a very dangerous way to give permission, this gives everyone in the world full control over file.

chown

chown is pretty straight forward. Just remember that the syntax used for ownership is owner:group

Here are few examples:

To make a user named bob the owner of folder called MyDirectory:

chown bob MyFolder

To make a group names myGroup the owner of MyDirectory folder (notice the colon before group name, remember the owner:group pattern):

chown :myGroup MyDirectory

To make a user named john and a group named group2 the owner of folder MyDirectory:

chown john:group2 MyDirectory
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