All about Unix groups and access control.

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151
votes
8answers
239k views

How do I remove a user from a group?

Which command should I use to remove a user from a group in Debian? When adding a user to a group, it can be done with: usermod -a -G group user However, I could not find a similar command (...
117
votes
6answers
41k views

Where did the “wheel” group get its name?

The wheel group on *nix computers typically refers to the group with some sort of root-like access. I've heard that on some *nixes it's the group of users with the right to run su, but on Linux that ...
67
votes
3answers
86k views

Make all new files in a directory accessible to a group

Suppose I have two users A and B and a group G and a folder foo, both users are members of G (using linux and ext3). If I save as user A a file under foo, the permissions are: -rw-r--r-- A A. ...
27
votes
2answers
49k views

Getting new files to inherit group permissions on Linux

I am having a problem with permissions on a Linux server. I am used to BSD. When a directory is owned by a group the user who owns it isn't in such as www-data, files created in it will be owned by ...
24
votes
3answers
18k views

How to apply changes of newly added user groups without needing to reboot?

Assume I'm logged in with user takpar: takpar@skyspace:/$ As root, I've added takpar as a member of group webdev using: # usermod -a -G webdev takpar But it seems it has not been applied. because ...
24
votes
2answers
92k views

How can I change a user's default group in Linux?

Being new to Linux administration, I'm a little confused about the following commands: useradd usermod groupadd groupmod I've just finished reading the user administration book in the Linux/Unix ...
20
votes
3answers
4k views

Typical use case for a group password

I checked more than half a century worth Unix experience and neither my colleagues, nor myself has ever set a password on a group (sg and gpasswd). What would be a typical use case for a group ...
18
votes
1answer
76k views

How to change primary group? [duplicate]

I have a user like this: uid=501(ironsand) gid=500(foo) groups=500(foo),10(wheel),497(git),501(ironsand) And to change primary group to ironsand like gid=501(ironsand), I typed this command: sudo ...
17
votes
3answers
63k views

Change gid of a specific group

I'd like to change group id of a specific group. There are so may solution for changing the gid of a file or directories. But that's not what I want. Is there a way to do that?
16
votes
2answers
13k views

Why is Debian not creating the 'wheel' group by default?

It appears to be Unix tradition that a wheel group is created automatically, but Debian (and children, naturally) doesn't do so. Is there a rationale somewhere? Where else have you seen this tradition ...
14
votes
3answers
55k views

granting write permissions to a group to a folder

How can I grant write permission to 1 group ? I have 2 users (alex and ben). alex is member of group alex and of group consult. ben is member of group ben and of group consult. I want to grant read ...
14
votes
1answer
7k views

In /etc/group what is the meaning of the second field?

A sample /etc/group file contains the following entries: root:*:0: adm:!:4:logcheck antoine:x:1000: The man pages I've read (Debian & OSX) says the second field is to store a group password. ...
14
votes
2answers
15k views

GID, current, primary, supplementary, effective and real group IDs?

The following links discuss these concepts in different contexts. I have read their definitions, but I still can't tell how they are related, or if some of them are just the same. Current group ID ...
14
votes
2answers
2k views

Why is root in wheel and operator? Can root being in a group ever make a difference?

I just noticed on my FreeBSD machine that root is in wheel and operator. I'm trying to think of a situation where UID 0 being in a group would have any effect on... well... anything, and I'm coming up ...
13
votes
4answers
969 views

Groups differ from the local ones when logging in remotely

We store our users in LDAP, alongside some groups that have meaning across different systems (organizational roles including wheel). There are also groups local to workstations, e.g. audio or video ...
12
votes
2answers
6k views

I can't delete a file that I have write permissions for as a group member

$ touch testfile $ chmod g+w testfile $ sudo adduser user2 user1 $ stat -c'%a %A' testfile 664 -rw-rw-r-- $ su user2 Password: $ groups user2 user1 $ rm testfile rm: cannot remove `testfile': ...
11
votes
1answer
10k views

Meaning of root:wheel

What does root:wheel mean in the following? chown root:wheel myfile
11
votes
3answers
31k views

How do i extend a partition with a LVM and the contained physical volume and logical volume?

On my 240 GB SSD i had at first two partitions, one containing the Logical Volume with Linux Mint and the other had contained a NTFS partition to share with Windows. Now i removed the NTFS partition ...
10
votes
5answers
13k views

Setting multiple groups as directory owners

On my server I have directory /srv/svn. Is it possible to set this directory to have multiple group ownerships, for instance devFirmA, devFirmB and devFirmC? The point is, I want to subversion ...
10
votes
1answer
16k views

Group within group file permissions

I tried finding this on here, but couldn't so sorry if it's a duplicate. Say I have 2 groups and a user: group1, group2, user1 with the following structure: group1 is a member of group 2, user1 is a ...
9
votes
2answers
4k views

Short, simple command to create a group if it doesn't already exist?

What is the cleanest way to modify this command in bash to only run if the group does not exist? groupadd somegroupname A one-liner would be best.
9
votes
2answers
8k views

What are the allowed group names for groupadd?

I followed these instructions to build Shadow, which provides the groupadd command. I am now getting an error when trying this: $ groupadd automake1.10 groupadd: 'automake1.10' is not a valid group ...
9
votes
1answer
10k views

what is 'nogroup' group's purpose

When I list al groups I see one called 'nogroup'. What is this for? Is it supposed to be least privileged one or something? I'm using ubuntu 11.04.
8
votes
3answers
18k views

What does GID mean?

What does GID actually mean? I have Googled it and this is what linux.about.com said: Group identification number for the process. Valid group numbers are given in /etc/group, and in the GID ...
8
votes
2answers
8k views

I added a user to a group, but group permissions on files still have no effect

I changed permissions of a file (chmod g+w testfile) and running ls -l testfile gives: -rwxrwxr-x 1 user1 user1 0 2011-01-24 20:36 testfile I then added a user to that group ("/etc/group" has user1:...
8
votes
1answer
1k views

File owner must belong to file group?

I have a rather simplistic understanding of file permissions on *nix systems. I understand that there is a file owner and file group, but is there a hard and fast rule on whether the said file owner ...
8
votes
1answer
3k views

How to run a process with a specific group?

I have to start an application with my own user rights, but the group must be different. So, instead of: $ ps -eo "user,group,args" | grep qbittorrent morfik morfik /usr/bin/qbittorrent it ...
8
votes
1answer
785 views

What is the purpose of `/etc/group-`

On a standard Linux distribution (e.g. Ubuntu) there is usually /etc/group and /etc/group-, where the second one is only readable by root. man group only describes /etc/group. Thus my question: What ...
8
votes
1answer
11k views

addgroup vs groupadd

I happen to know there is a slight difference between adduser and useradd. (i.e., adduser has additional features to useradd, such as creating a home directory.) Then what is the relation between ...
8
votes
3answers
4k views

Can't read a file although it's in my group and permissions for group read are set

I encounter a strange problem on a unix/linux machine: I'm member of a group, let's call it group A and a certain file (which has a different owner) belongs to group A as well. The permissions of ...
8
votes
2answers
8k views

Group member cannot write even with write permission

The logged in user is a member of a group that has a write permission on a folder. But when this user is trying to write something, "permission is denied". The log below summarizes the question: ...
7
votes
2answers
12k views

What is nobody user and group?

On my server (Synology DS212) some files and folders have nobody nobody users and groups. What are the characteristics of this user and group? Who can write of read this file? How can I change it ? ...
7
votes
4answers
4k views

Reasons behind the default groups and users on Linux

Having a look at the default users & groups management on some usual Linux distributions (respectively ArchLinux and Debian), I'm wondering two things about it and about the consequences of ...
7
votes
4answers
387 views

Groupwise uniq command?

I am searching for a command to get from a file in this format: hello 32 hello 67 hi 2 ho 1212 ho 1390 ho 3000 To this format (deduplicate by taking the last row of a "group"): hello ...
7
votes
5answers
293 views

Changing Unix group for files

I have a file that a colleague and I are editing together, on a Unix system. We are using Unix group permissions to edit it. We have one Unix group that we are both members of. Whenever I save the ...
7
votes
1answer
4k views

Why cannot a user change group ownership of his own files? [duplicate]

Why cannot a user change the group permissions of files which he owns. Let's suppose I have user martin: $ ls -lAd /home/martin/ drwx------ 8 martin martin 4096 Apr 20 01:06 /home/martin/ For some ...
7
votes
3answers
6k views

What does it mean to be in group 0?

Several users in a system I inherited have their group set to 0 in /etc/passwd. What does that mean? Do they essentially get full root privileges? The system is running CentOS 5, and the users ...
7
votes
1answer
2k views

Why does every user have his own group?

One thing I've noticed in a lot of recent distros is that users all have their own groups with the same name as their user name. What's the purpose of that? Groups are made to group users together in ...
7
votes
1answer
7k views

Give default write permission to group to any newly created files and folders

Let's say that we have 2 users: a and b, that are both part of group general. I would like that any file or folder that A creates, would have write permission to the group GENERAL. How can I do it? ...
6
votes
2answers
9k views

Add all users in one group to another group?

I have some users in a group called aa and I need to give them the rights to write to a folder which is currently tomcat:tomcatdeploy. The straightforward way to do this is to add all the users to ...
6
votes
5answers
3k views

Why is it recommended to create a group and user for some applications?

Most of the time, when installing a program from source it is recommended to create a new user and a new group and give /usr/local/<myapp> the recently created user and group ownership. Why is ...
6
votes
2answers
13k views

wireshark: Couldn't run /usr/sbin/dumpcap in child process [duplicate]

Possible Duplicate: How to add write permissions for a group? When I run Wireshark, It shows the following message: Couldn't run /usr/sbin/dumpcap in child process: Permission denied Are you ...
6
votes
3answers
4k views

how to login as a member of specific group

i want to login as a member of non primary group to create files whose owner as a member of non primary group of current user. -rwxr-xr-x 2 gowtham gowtham 4096 Sep 5 14:48 defaultNewFile ...
6
votes
1answer
227 views

When a member of multiple groups, how do I set the default group for newly created files?

With umask, I can determine the permissions for newly created files. But if I am a member of multiple groups, how do I set the default group for newly created files? This question seems relevant, ...
6
votes
2answers
1k views

groupadd failure while writing changes to /etc/group

I have been following this guide on installing debian-kit on my Sony Xperia Tablet Z and the installation goes fine until I try to apt-get install andromize which fails with the error groupadd: ...
5
votes
3answers
2k views

Precedence of user and group owner in file permissions

I just ran into something unexpected (for me) regarding file permissions on Linux (Arch Linux). Basically I have: userX in groupX fileX userX:groupX ---rwx---- What puzzles me: I cannot perform ...
5
votes
3answers
4k views

How to restrict a user to one folder and not allow them to move out his folder

I have ubuntu server on digitalocean and I want to give someone a folder for their domain on my server, my problem is, I don't want that user to see my folders or files or to be able to move out their ...
5
votes
2answers
2k views

Group memberships and setuid/setgid processes

Processes which de-escalate privileges via setuid() and setgid() do not seem to inherit the group memberships of the uid/gid they set. I have a server process that must be executed as root in order ...
5
votes
2answers
4k views

Problem while running “newgrp” command in script

I want to change the working group in my script. So I wrote a line newgrp test_grp1 in my script. But my script is automatically exited after running this line. Are there any solution to overcome this ...
5
votes
1answer
1k views

Adding a system user to an LDAP group with SSSD

Our LDAP server is running RFC 2307 groups (memberuid contains a username, not a DN). With our old nscd/nss_ldap/pam_ldap setup, you could list a non-LDAP user (a system user from /etc/passwd) in an ...