Change user id and group id ownership of files within a tarball

tarusers

I have a tarball and the files it contains do not have the right user and group ownership. Files are owned jenkins:jenkins and I'd like them to be owned naftuli:othergroup.

Is there a way for me to edit the tarball in place so that the files it contains become owned by naftuli:othergroup?

The problem I'm facing is that at the time of the tarball creation, the jenkins user doesn't have permissions to chown things to different users and groups. At the time of extraction, I will have permissions to create those files as the users mentioned, so I need to edit the user ids and group ids within the tarball.

Best Answer

Archive::Tar or similar software would be one method.

% touch foo  
% tar cvf x foo
foo
% tar tvf x          
-rw-rw-r--  1 jdoe12   jdoe12           0 May  6 20:36 foo
% perl -MArchive::Tar -e '$t=Archive::Tar->new;$t->read("x");$t->chown("foo","root");$t->write("y")'
% tar tvf y
-rw-rw-r--  1 root     jdoe12           0 May  6 20:36 foo
%

Related Solutions

Linux Permissions – Group Within Group File Permissions Explained

There is no such thing as a group being a member of a group. A group, by definition, has a set of user members. I've never heard of a feature that would let you specify “subgroups” where members of subgroups are automatically granted membership into the supergroup on login. If /etc/group lists group1 as a member of group2, it designates the user called group1 (if such a user exists, which is possible: user names and group names live in different name spaces).

If you want user1 to have access to file2, you have several solutions:

Make file2 world-accessible (you probably don't want this)
Make user1 the owner of file2: chown user1 file2
Add user1 to group2: adduser user1 group2
Add an ACL to file2 that grants access to either user1 or group`:
```
setfacl -m user:user1:rw file2
setfacl -m group:group1:rw file2
```
See Make all new files in a directory accessible to a group on enabling ACLs.

Files Permissions – What is Nobody User and Group?

The nobody user is a pseudo user in many Unixes and Linux distributions. According to the Linux Standard Base, the nobody user and its group are an optional mnemonic user and group. That user is meant to represent the user with the least permissions on the system. In the best case that user and its group are not assigned to any file or directory (as owner). This user is in his corresponding group that is (according to LSB) also called "nobody" and in no other group.

In earlier Unixes and Linux distributions daemon (for example a webserver) were called under the nobody user. If a malicious user gained control over such a daemon, the damage he can perform is limited to what the daemon can. But the problem is, when there are multiple daemons running with the nobody user, this has no sense anymore. That's why today such daemons have their own user.

The nobody user should have no shell assigned to it. Different distributions handle that in different ways: some refer to /sbin/nologin that prints a message; some refer to /bin/false that simply exits with 1 (false); or some just disable the user in /etc/shadow.

According to Linux Standard Base, the nobody user is "Used by NFS". In fact the NFS daemon is one of the few that still needs the nobody user. If the owner of a file or directory in a mounted NFS share doesn't exist at the local system, it is replaced by the nobody user and its group.

You can change the permission of a file owned by the nobody user just simply with the root user and chown. But at the machine hosting the NFS share, that user might exist, so take care.

I also use a Synology system. They run the apache web-server under the nobody user.

Best Answer

Related Solutions

Linux Permissions – Group Within Group File Permissions Explained

Files Permissions – What is Nobody User and Group?

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