Check users permissions linux

How to check permissions of a specific directory?

I know that using ls -l «directory/directory/filename» tells me the permissions of a file. How do I do the same on a directory? I could obviously use ls -l on the directory higher in the hierarchy and then just scroll till I find it but it’s such a pain. If I use ls -l on the actual directory, it gives the permissions/information of the files inside of it, and not of the actual directory. I tried this in the terminal of both Mac OS X 10.5 and Linux (Ubuntu Gutsy Gibbon), and it’s the same result. Is there some sort of flag I should be using?

10 Answers 10

-d, --directory list directory entries instead of contents, and do not dereference symbolic links 

You might be interested in manpages. That’s where all people in here get their nice answers from.

I think the man page is poorly worded. I scoured it five times before I started googling. I don’t want directory ‘entries’ (thing ‘entered’ into directories? Like their files and sub-directories?) nor their ‘contents’ (they sound like the same concept to me), I want the directories themselves.

it’s completely standard terminology, the directories themselves are the directory entries, i.e. entries in the filesystem

It may be standard terminology, but to someone who would likely be asking such a question, it is probably confusing jargon.

You can also use the stat command if you want detailed information on a file/directory. (I precise this as you say you are learning ^^)

— indicates the beginning of the command options.

l asks for a long list which includes the permissions.

d indicates that the list should concern the named directory itself; not its contents. If no directory name is given, the list output will pertain to the current directory.

In GNU/Linux, try to use ls , namei , getfacl , stat .

For Dir

[flying@lempstacker ~]$ ls -ldh /tmp drwxrwxrwt. 23 root root 4.0K Nov 8 15:41 /tmp [flying@lempstacker ~]$ namei -l /tmp f: /tmp dr-xr-xr-x root root / drwxrwxrwt root root tmp [flying@lempstacker ~]$ getfacl /tmp getfacl: Removing leading '/' from absolute path names # file: tmp # owner: root # group: root # flags: --t user::rwx group::rwx other::rwx [flying@lempstacker ~]$ 

[flying@lempstacker ~]$ stat -c "%a" /tmp 1777 [flying@lempstacker ~]$ stat -c "%n %a" /tmp /tmp 1777 [flying@lempstacker ~]$ stat -c "%A" /tmp drwxrwxrwt [flying@lempstacker ~]$ stat -c "%n %A" /tmp /tmp drwxrwxrwt [flying@lempstacker ~]$ 

For file

[flying@lempstacker ~]$ ls -lh /tmp/anaconda.log -rw-r--r-- 1 root root 0 Nov 8 08:31 /tmp/anaconda.log [flying@lempstacker ~]$ namei -l /tmp/anaconda.log f: /tmp/anaconda.log dr-xr-xr-x root root / drwxrwxrwt root root tmp -rw-r--r-- root root anaconda.log [flying@lempstacker ~]$ getfacl /tmp/anaconda.log getfacl: Removing leading '/' from absolute path names # file: tmp/anaconda.log # owner: root # group: root user::rw- group::r-- other::r-- [flying@lempstacker ~]$ 

[flying@lempstacker ~]$ stat -c "%a" /tmp/anaconda.log 644 [flying@lempstacker ~]$ stat -c "%n %a" /tmp/anaconda.log /tmp/anaconda.log 644 [flying@lempstacker ~]$ stat -c "%A" /tmp/anaconda.log -rw-r--r-- [flying@lempstacker ~]$ stat -c "%n %A" /tmp/anaconda.log /tmp/anaconda.log -rw-r--r-- [flying@lempstacker ~]$ 

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Linux File Permission Tutorial: How to Check and Change Permissions

Linux, like other Unix-like operating systems, allows multiple users to work on the same server simultaneously without disrupting each other.

Individuals sharing access to files pose a risk exposing classified information or even data loss if other users access their files or directories. To address this, Unix added the file permission feature to specify how much power each user has over a given file or directory.

In this tutorial, you will learn how to view and change file permissions in Linux.

How to View Check Permissions in Linux

To start with file permissions, you have to find the current Linux permission settings. There are two options to choose from, depending on your personal preference: checking through the graphical interface or using the command.

Check Permissions using GUI

Finding the file (directory) permission via the graphical user interface is simple.

1. Locate the file you want to examine, right-click on the icon, and select Properties.

2. This opens a new window initially showing Basic information about the file.
Navigate to the second tab in the window, labeled Permissions.

3. There, you’ll see that the permission for each file differs according to three categories:

• Owner (the user who created the file/directory)
• Group (to which the owner belongs to)
• Others (all other users)

For each file, the owner can grant or restrict access to users according to the categories they fall in.

In our example, the owner of the file test.txt has access to “Read and write”, while other members of its group, as well as all other users, have “Read-only” access. Therefore, they can only open the file, but cannot make any modifications.

To alter the file configuration, the user can open the drop-down menu for each category and select the desired permission.

Additionally, you can make the file executable, allowing it to run as a program, by checking the Execute box.

Check Permissions in Command-Line with Ls Command

If you prefer using the command line, you can easily find a file’s permission settings with the ls command, used to list information about files/directories. You can also add the –l option to the command to see the information in the long list format.
To check the permission configuration of a file, use the command:

For instance, the command for the previously mentioned file would be:

As seen in the image above, the output provides the following information:

• file permission
• the owner (creator) of the file
• the group to which that owner belongs to
• the date of creation.

It shows the permission settings, grouped in a string of characters (-, r, w, x) classified into four sections:

1. File type. There are three possibilities for the type. It can either be a regular file (–), a directory (d) or a link (i).
2. File permission of the user (owner)
3. File permission of the owner’s group
4. File permission of other users

The characters r, w, and x stand for read, write, and execute.
The categories can have all three privileges, just specific ones, or none at all (represented by –, for denied).

Users that have reading permission can see the content of a file (or files in a directory). However, they cannot modify it (nor add/remove files in a directory). On the other hand, those who have writing privileges can edit (add and remove) files. Finally, being able to execute means the user can run the file. This option is mainly used for running scripts.

In the previous example, the output showed that test.txt is a regular file with read and write permission assigned to the owner, but gives read-only access to the group and others.

Using Chmod Command to Change File Permissions

As all Linux users, you will at some point need to modify the permission settings of a file/directory. The command that executes such tasks is the chmod command.

chmod [permission] [file_name]

There are two ways to define permission:

1. using symbols (alphanumerical characters)
2. using the octal notation method

Define File Permission with Symbolic Mode

To specify permission settings using alphanumerical characters, you’ll need to define accessibility for the user/owner (u), group (g), and others (o).

Type the initial letter for each class, followed by the equal sign (=) and the first letter of the read (r), write (w) and/or execute (x) privileges.

To set a file, so it is public for reading, writing, and executing, the command is:

chmod u=rwx,g=rwx,o=rwx [file_name]

To set permission as in the previously mentioned test.txt to be:
• read and write for the user
• read for the members of the group
• read for other users

Use the following command:

Note: There is no space between the categories; we only use commas to separate them.

Another way to specify permission is by using the octal/numeric format. This option is faster, as it requires less typing, although it is not as straightforward as the previous method.

Instead of letters, the octal format represents privileges with numbers:

The privileges are summed up and depicted by one number. Therefore, the possibilities are:

• 7 – for read, write, and execute permission
• 6 – for read and write privileges
• 5 – for read and execute privileges
• 4 – for read privileges

As you have to define permission for each category (user, group, owner), the command will include three (3) numbers (each representing the summation of privileges).

For instance, let’s look at the test.txt file that we symbolically configured with the chmod u=rw,g=r,o=r test.txt command.

The same permission settings can be defined using the octal format with the command:

Define File Permission in Octal/Numeric Mode

Note: If you need a more in-depth guide on how to use Chmod In Linux to change file permissions recursively, read our Chmod Recursive guide.

Changing User File and Group Ownership

Aside from changing file permissions, you may come across a situation that requires changing the user file ownership or even group ownership.

Performing either of these tasks requires you first need to switch to superuser privileges. Use one of the options outlined in the previous passage.

To change the file ownership use the chown command:

chown [user_name] [file_name]

Instead of [user_name] type in the name of the user who will be the new owner of the file.

To change the group ownership type in the following command:

chgrp [group_name] [file_name]

Instead of [group_name] type in the name of the group that will be the new owner of the file.

Learning how to check and change permissions of Linux files and directories are basic commands all users should master. To change file’s group permissions, you might find helpful our article on how to use the chgrp command.

No matter whether you prefer using the GUI or command-line, this article should help you better understand how to use file permissions.

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How do you view file permissions?

I want to know how to see the permissions a particular file has. Which command should I type in the terminal? However, I don’t want to change it.

4 Answers 4

If you want to see the the permission of a file you can use ls -l /path/to/file command.

 ls -l acroread -rwxr-xr-x 1 10490 floppy 17242 May 8 2013 acroread 

What does this mean ?

First — represents a regular file. It gives you a hint of the type of object it is. It can have following values.

• d (directory)
• c (character device)
• l (symlink)
• p (named pipe)
• s (socket)
• b (block device)
• D (door)
• — (regular file)

r represents read permission.
w represents write permission and
x represents executable permission.

First combination of rwx represents permission for the owner .
Second combination of rwx represents permission for the group .
Third combination of rwx represents permission for the other of the file.

Octal notation

Permission of file can also be represented in octal notation.
In octal notation

Read or r is represented by 4,
Write or w is represented by 2
Execute x is represented by 1.

Sum of these three is use to represent the permission.

stat command can be used to view file permission in octal notation

 stat -c "%a %n" acroread 755 acroread 

For owner it is 4+2+1=7 (111 in binary)
For group it is 4+0+1=5 (101 in binary) and
For other it is 4+0+1=5 (101 in binary).

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Check if different user has read/write permissions to a file on linux

will return 0 if otheruser can read the file, or 1 if otheruser cannot read the file. You can run test -r /path/to/file; echo «$?» to view the return code of the test command.

Use test -w to test for write permission and test -x to test for execute permission.

Test Read Permission

Attempt to read the beginning of the file and discard the normal output. You can then look for an empty string (success) or a «Permission denied» message (you can also check for other error messages such as «No such file or directory»). For example:

head -1 /path/to/file 2>&1 > /dev/null | grep 'Permission denied' 

Test Write Permission

Use the touch command with the -c (—no-create) option. Combine stdout and stderr and again search for an empty string (success) or an error:

touch -c /path/to/file 2>&1 | grep 'Permission denied' 

If you’re explicitly testing write access of a directory, be sure to test the directory and not a file contained within, since with the -c option, there’s no error condition if the file doesn’t exist even in a directory you don’t have write access to:

-c, if the file does not exist, do not create it and do not report this condition

Test As Specific User

The final piece of the puzzle is how to check this as a different user. As root execute the test command as the desired user with «sudo -u [username] [command]» so using your suggested user:

sudo -u apache touch -c /path/to/file 2>&1 

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