Anything related with user accounts and user management on Unix-like systems.

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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:...
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 ...
15
votes
1answer
3k views

Can one PC be used by two users at the same time via dual-monitor?

Since modern PCs can use two screens at the same time I wonder if it is possible to plug in two keyboards and mouses as well to have the two screens run two (more or less) independent X-sessions at ...
10
votes
2answers
4k views

How to restrict internet access for a particular user on the lan using iptables in Linux

Let's say there are two users on the LAN, A and B. How do I restrict user A from internet access using iptables rules and saving the rules so that after reboot, they are still effective. And suppose I ...
36
votes
2answers
32k views

What does adduser do that useradd doesn't?

In addition to the more widespread useradd, Debian based systems also contain an additional adduser command which provides a higher level interface for adding users and some related tasks. There are ...
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 ...
14
votes
10answers
2k views

Concern about logging in as root overrated?

For personal linux on my personal notebooks, I've usually set my environment to autologin as root even under X or lower runlevels. I've found my workflow is very pleasant and fast, without any ...
15
votes
5answers
40k views

Disable user shell for security reasons

We have several user accounts that we create for automated tasks that require fine-grained permissions, such as file transfer across systems, monitoring, etc. How do we lock down these user accounts ...
20
votes
2answers
31k views

How to create a user with limited RAM usage?

So I have 4 GB RAM + 4GB swap. I want to create a user with limited ram and swap: 3 GB RAM and 1 GB swap. Is such thing possible? Is it possible to start applications with limited RAM and swap ...
47
votes
5answers
80k views

Disable a user's login without disabling the account

Let's say I create a user named "bogus" using the adduser command. How can I make sure this user will NOT be a viable login option, without disabling the account. In short, I want the account to be ...
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 ...
12
votes
2answers
39k views

How to add a ssh user who only has permissions to access specific folder?

How to add an ssh user who only has permissions to access specific folder? useradd -d /var/www/xyz.com.tr/musteri -s /bin/bash -g sshd musteri I created a user called musteri. I set its home ...
0
votes
1answer
657 views

Added user supplementary group, but 'groups(1)' not showing change [duplicate]

I'm trying to add myself to the fuse user group but it doesn't look like the change is taking effect even though /etc/group looks correct after invoking addgroup or usermod. I've tried both ... sudo ...
5
votes
1answer
58k views

How can I create an SFTP user in CentOS?

I'd like to give temporary SFTP access to a support guy. How do I create an SFTP user? And how can I delete it once the job is done? Also, how do I specify a home directory for them? Can I prevent ...
27
votes
3answers
14k views

How can I determine if someone's SSH key contains an empty passphrase?

Some of my Linux & FreeBSD systems have dozens of users. Staff will use these "ssh gateway" nodes to SSH into other internal servers. We're concerned that some of these people use an unencrypted ...
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 ? ...
10
votes
7answers
3k views

Is it bad practice to set root's shell to something other than the default?

Once a friend of mine (who is an experienced Unix/Linux user) told me that setting root's shell to something other than sh (i.e bash or zsh) might create problems, because some script might assume ...
2
votes
2answers
1k views

What does the `who` command result `root :0` mean?

The return value of command who will always include root :0 in X Window pts. I guess it actually means the GNOME login. Am I right? Another question is where to get this knowledge, as I don't see it ...
70
votes
5answers
22k views

What are other ways to share a tmux session between two users?

I'm looking for a clean and easy way to share a tmux session with another user on the same machine. I've tried the -S socket-path option, but it requires opening up all permissions of the socket-path ...
31
votes
2answers
90k views

What user should apache and PHP be running as? What permissions should /var/www files have?

I just spun up an Ubuntu 11.10 box and then ran apt-get install apache2 php5 to install apache2 and PHP 5 on the box. Now it is functioning as a "web server" and it loads the "It Works!" page. Now I'm ...
40
votes
7answers
38k views

How do you kick a benign user off your system?

I was googling this a bit ago and noticed a couple of ways, but I'm guessing that google doesn't know all. So how do you kick users off your Linux box? also how do you go about seeing they are logged ...
43
votes
7answers
25k views

Does /usr/sbin/nologin as a login shell serve a security purpose?

In my /etc/passwd file, I can see that the www-data user used by Apache, as well as all sorts of system users, have either /usr/sbin/nologin or /bin/false as their login shell. For example, here is a ...
39
votes
4answers
24k views

Is it possible to rename a Unix user account?

I installed Ubuntu on a computer that is now used by somebody else. I renamed the account with her name, but it only changes the fullname, not the user name, which is still displayed in the top right (...
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 ...
44
votes
2answers
27k views

What's the difference between a normal user and a system user?

Some documentation I'm going through has a boolean switch on whether or not a user is a 'system' user or a 'normal' user defaulting to 'normal'). What is the difference between these two modes of ...
12
votes
5answers
27k views

Can a linux user change their password without knowing the current password?

I'm setting up a few ubuntu boxes, and using opscode's chef as a configuration tool. It would be fairly easy to install public keys for each user on each of these servers, and disable password ...
11
votes
3answers
13k views

How can I create automatically expiring user accounts?

This is what I'd like to be able to do: After a user's account is created, they should be able to ssh-tunnel, but their account is automatically removed after 30 days unless the countdown is reset by ...
10
votes
1answer
17k 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 ...
5
votes
2answers
4k views

Find files created by a particular user

How would I go about discovering all of the files created by a particular user and display them to the screen? I've started a script that prompts the current user to enter the username of whom they ...
8
votes
1answer
815 views

Lightweight virtualization on Linux with user isolation

What Linux-on-Linux virtualization technologies provide user isolation? Specifically, I want root in the virtual machine not to have any privilege on the host. This was not the case for LXC, but was ...
8
votes
3answers
1k views

Does character 'ä' in usernames cause bugs in linux systems?

I want to use my first name as an username but it contains character 'ä'. I found this thread. Now I understand, why some some characters are disabled, but what about 'ä'? Can this character cause ...
5
votes
2answers
61 views

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

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 ...
5
votes
3answers
531 views

Unix users, groups, and permissions

I don't understand unix users, groups, permissions, etc. For example, things managed by the chmod, chgrp, usermod, groupadd, etc. commands. How do all these things work?
4
votes
3answers
4k views

How to find the machine from which a user logged into current machine using ssh?

In a multi server architecture, is it possible to find out from which machine a user logged into current machine using ssh? For example, user1 logged into host1. From there, the user logged into ...
15
votes
3answers
9k views

Creating a user who cannot get an interactive shell

What are interactive and non-interactive shell? Questions: Create a user john who should not get an interactive shell. How can we do this?
12
votes
4answers
9k views

What are the dangers of creating a normal user with UID < 500?

What are the dangers of creating a normal user with UID < 500? Assuming the UID's are not duplicates of existing UID's, what could go wrong? This is not something that I want to do, but something ...
7
votes
2answers
3k views

How to set permissions in /sys/ permanent?

I'm starting X as a user and need to set my keyboard brightness in /sys/class/leds/asus\:\:kbd_backlight/brightness. The /sys/ directory gets recreated after reboot, so the permissions will reset too. ...
5
votes
2answers
6k views

Local Account Creation Date

For compliance purposes there is the need to fetch information regarding local (user and non-user) accounts creation date on UNIX machines. Is there any way (even if it's not the most reliable or ...
4
votes
4answers
225 views

“Who” prints duplicated usernames

This is result of who -uH: NAME LINE TIME IDLE PID COMMENT me :0 2013-08-29 01:29 ? 1686 (:0) me pts/0 2013-08-29 01:42 old ...
4
votes
3answers
2k views

What mechanism prevents any user from accessing any other user's files via root?

On a multi-user system, what protects against any user accessing any other users files via root? As context, the question is based on my understanding as follows: There are two commands related to ...
3
votes
1answer
3k views

User logged in by sftp does not show up in `w`

My server is Centos 5. I have a chroot environment set up with the following in my sshd_config Match group sftponly ForceCommand internal-sftp ChrootDirectory %h AllowTcpForwarding no ...
3
votes
1answer
510 views

Ubuntu user disappeared from machine

Unsolved mystery - I was given a coworker's Ubuntu 12.04.1 LTS machine and set up my own (sudo/admin) user on there from the command line. I switched to my user (from his sudo/admin user) and ...
2
votes
2answers
62 views

When opening a terminal does not require a login?

Speaking about Linux and in particular Ubuntu (from 14.04) systems: Case 1 - As pointed out in this answer, processes that allocate a pseudo-terminal don't need to make a login: for example, cups. ...
2
votes
1answer
249 views

Where can I find a reference to the format of the comment field (field 5) of the /etc/passwd file?

In the /etc/passwd file on my system, the "comment" field, field 5, is inconsistent in its contents. I thought that I could extract it to get the full name of the user. fullname=`awk -F: '$1 == name ...
2
votes
1answer
574 views

Unable to preserve ownership in a copy but able with a move?

I have noticed that I am unable to preserve ownership if I rsync -o files. However, I am when I move them. This is all without admin privileges. What is the rationale of this? Several threads e.g. (1)...
2
votes
2answers
6k views

Disable operations outside user's home directory with chroot jail?

I'm trying to restrict a user to a specific directory called gclegal using a chroot jail. I've uncommented the line in the /etc/vsftpd.conf file chroot_local_user=YES Created a new user called kg: ...
0
votes
1answer
98 views

list users who are all created by current user in linux

I have set of users with root access.I want to know list of users who are all created by currently logged in user. From below structure if user1 login to system , how to list user's like user11,...
208
votes
8answers
790k views

How to switch between users on one terminal?

I'd like to log in as a different user without logging out of the current one (on the same terminal). How do I do that?
20
votes
5answers
29k views

User-friendly command to list all users on Ubuntu system?

Is there a user-friendly command I can use to list users in a console on an Ubuntu system? When I cat /etc/passwd I get a hard-to-read list of users. It would be nice to see an alphabetized list, ...
7
votes
3answers
21k views

How to create an unprivileged user in CentOS?

I want to create an unprivileged user to run my RhodeCode server and Celery daemon on a CentOS instance. I think the accepted definition of this is no home directory, login disabled, and no shell ...