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I have a file "abc" with permissions 440 .The owner of this file is "root" and the group of this file is "groupabc" . I have a user "user1" .Is their anyway I can see the contents of files "abc" using the user "user1" ?

I don't have the root password.

What comes to my mind is that since file "abc" belongs to the group "groupabc" ,so if I can add the user "user1" to the group "groupabc". I should be able to view the contents of the file "abc". I tried command usermod ,but since I don't have the sudo access ,It didn't work.Is their anyway I can view the contents of the file "abc".

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Hi...Is there anything called guest group in unix. I see the contents of /etc/groups as below.Does this have any special meaning ? guest:x:1014: groupabc:x:1024:guest –  user1743613 Nov 16 '12 at 21:33
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You could easily create a group called guest but it probably wouldn't have any special significance - it's just a normal group. How is this relevant to the question? –  jw013 Nov 16 '12 at 21:35
    
You will need root to give you access (either as root, or as the owner of the file). That's the whole point of permissions. –  Gilles Nov 16 '12 at 22:04
    
The group administrator can also add you to the group, if there have one. –  Edw4rd Nov 16 '12 at 23:21
    
You should ask the person that administers your machine. They will have root access. Otherwise, the /tmp folder may be used for sharing files with other users temporarily, as the folder name suggests. –  vgoff Nov 17 '12 at 0:14
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1 Answer

If the goal is to allow user1 to read file abc whose permissions and ownership attributes are as you describe, you need to do one of the following:

  • change the file ownership (so that user1 or a group that contains user1 owns the file), or

  • change the permissions so the file is world readable, allowing everyone including user1 to read it, or

  • add user1 to group groupabc.

Unfortunately, you need superuser (root) privileges to do any of the above, so without that you are out of luck within the constraints of the conventional Unix access control scheme.

Since your question is "is there any way ...?", there are other more indirect ways. You could ask a human in control of root for permission to read the file. Assuming the file system is not encrypted and you have physical access, you could reboot into another OS where you do have root access (e.g. a live CD / USB) and mount the file system there. Shadier methods probably exist as well.

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Is their any concept of open group in unix, I mean a group that is open to all and any user can assign itself to that group. –  user1743613 Nov 17 '12 at 11:44
    
@user1743613 No, there is no such thing. Only root can add users to groups. –  jw013 Nov 17 '12 at 16:43
    
Well, there is on systems that support gshadow. Then, it's just a matter of doing gpasswd that-group (as root or any administrator of that group), provide with an empty password. Then, any user can start a new process with that-group as the gid with the newgrp or sg commands. –  Stephane Chazelas Nov 19 '12 at 21:01
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