After you’ve worked with Linux for a while, you are almost sure to get a Permission Denied message. Permissions associated with files and directories in Linux were designed to keep users from accessing other users’ private files and to protect important system files.
The nine bits assigned to each file for permissions define the access that you and others have to your file.
Permission bits appear as rwxrwxrwx. The first three bits apply to the owner’s permission, the next three apply to the owner’s group, and the last three apply to all others. The r stands for read, the w stands for write, and the x stands for execute permissions. If a dash appears instead of the letter, it means that permission is turned off for that associated read, write, or execute.
You can see the permission for any file or directory by typing the ls −ld command. The named file or directory appears as those shown in the example below:
$ ls −ld ch3 test
−rw−rw−r−− 1 chris sales 4983 Jan 18 22:13 ch3
drwxr−xr−x 2 chris sales 1024 Jan 24 13:47 test
The first line shows a file (ch3) that has read and write on for the owner and the group. All other users have read permission, which means they can view the file but cannot change its contents or remove it. The second line shows a directory (indicated by the letter d before the permission bits). The owner has read, write, and execute permission, while the group and other users have only read and execute permissions. As a result, only the owner can add, change, or delete files in that directory. Any other user, however, can only read the contents, change to that directory, and list the contents of the directory.
If you own a file, you can change the permission on it as you please. You can do this with the chmod command. For each of the three sets of permission on a file (read, write, and execute), the r is assigned to the number 4, w to 2, and x to 1. So to make permissions wide open for yourself as owner, you would set the first number to 7 (4 plus 2 plus 1). The same would be true for group and other permission. Any combination of permissions can result from 0 (no permission) through 7 (full permission).
Here are some examples of how to change permission on a file and what the resulting permission would be:
chmod 777 files -> rwxrwxrwx
chmod 755 files -> rwxr−xr−x
chmod 644 files -> rw−−r—−r−−
chmod 000 files -> −−−−−−−−−
The nine bits assigned to each file for permissions define the access that you and others have to your file.
Permission bits appear as rwxrwxrwx. The first three bits apply to the owner’s permission, the next three apply to the owner’s group, and the last three apply to all others. The r stands for read, the w stands for write, and the x stands for execute permissions. If a dash appears instead of the letter, it means that permission is turned off for that associated read, write, or execute.
You can see the permission for any file or directory by typing the ls −ld command. The named file or directory appears as those shown in the example below:
$ ls −ld ch3 test
−rw−rw−r−− 1 chris sales 4983 Jan 18 22:13 ch3
drwxr−xr−x 2 chris sales 1024 Jan 24 13:47 test
The first line shows a file (ch3) that has read and write on for the owner and the group. All other users have read permission, which means they can view the file but cannot change its contents or remove it. The second line shows a directory (indicated by the letter d before the permission bits). The owner has read, write, and execute permission, while the group and other users have only read and execute permissions. As a result, only the owner can add, change, or delete files in that directory. Any other user, however, can only read the contents, change to that directory, and list the contents of the directory.
If you own a file, you can change the permission on it as you please. You can do this with the chmod command. For each of the three sets of permission on a file (read, write, and execute), the r is assigned to the number 4, w to 2, and x to 1. So to make permissions wide open for yourself as owner, you would set the first number to 7 (4 plus 2 plus 1). The same would be true for group and other permission. Any combination of permissions can result from 0 (no permission) through 7 (full permission).
Here are some examples of how to change permission on a file and what the resulting permission would be:
chmod 777 files -> rwxrwxrwx
chmod 755 files -> rwxr−xr−x
chmod 644 files -> rw−−r—−r−−
chmod 000 files -> −−−−−−−−−
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