Linux Commands Examples

A great documentation place for Linux commands


print the user names of users currently logged in to the current host


users [OPTION]... [FILE]

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Is there a way in Linux to update the user/group properties without having to login again?

I've read before that the newgrp command does this, but only for the current shell. There doesn't seem to be a better alternative than to log out and back in again.


Why do some packages require their own user to run?

Because the authors of those programs choose to use separate user databases rather than using the system password database.

One reason why that is sometimes done is if the program needs to have access to the plaintext version of the password, perhaps because it is implementing a network protocol which requires that, as there is no way to access the plaintext passwords for system users as they are only held in hashed form.

That is true for example with apache, and by extension for svn when it is using HTTP basic authentication, as HTTP basic authentication requires access to the plaintext passwords.


How to switch users without entering password

Did you try link text. This is a little dangerous if you don't know how to handle the shadow password file, however, probably the simplest way to do what you want.


Why does my Linux prompt show a $, instead of the login name and path?

You need to set a variable called PS1 on one of your login script, for example /etc/profile or ~/.bashrc. It will depend on your distribution.



Duplicating Linux-like user account permissions in Windows 7

Left in it's default configuration, running an account with USER permissions on Windows 7 will have essentially the effect you're describing, gmunk.

User Access Control (UAC) and the default rights of a USER account set account permissions more or less exactly as you describe. No special configuration necessary.


It depends. As always.

Depending on what you're doing with the computer your security requirements will change.

  • Is this a home computer that will be the only computer in the house? Add some antivirus software and you're pretty much OK.
  • Is this a corporate workstation? If the corporate network is secured properly, the security of individual workstations within the network is less important and is usually turned down a little to enable communication with the rest of the network.
  • Is this a desktop that will not move and will always be connected to the same network? Probably somewhere between the corporate setup and the single-computer home setup. You'll want to be able to share printers and maybe files and media between the computers, so you'll want to make sure they trust each other but don't accept communication from non-trusted computers as well as more robust antivirus.
  • Is this a laptop that will be traveling? You'll want really, really strong security. A local firewall installed on the computer (the Windows firewall is OK, you may prefer something else though) and good antivirus software.
  • Does the user need to be able to install stuff? Probably not based on your question.

Linux username@server disappears after login as root

Do a few exit commands. Your su root started a subshell where you're root, and your su user started another. Typing exit will end those subshells and bring you back where you started -- one level deep.


Linux groups for standard user

You don't need to have users members of any of them to get a functioning desktop, however, you may wish to add them to some for convenience.

The audio and video groups allow the user to make changes to sound and display settings.

The cdrom group allows the user to eject the cdrom.

The users group is a ready made group for sharing. If all users are members of this group, they can create files with the :users group name, and then add permissions to allow others to access them.

The sudo group allows the user to escalate to root (if sudo is installed) for as single command, or for multiple commands.

The dialout group is useful if you are on laptop and have a modem.

The plugdev group allows popups for removable devices, and to manage them.


How to set up virtual users in vsftpd?

Maybe you forgot to give your ftp user read/write permission to /var/www/sites/$user ?

Try following this guide for setting up the server:

I have used it a couple of months ago with good results.


Creating a Linux utility : users/groups/permissions best practice

For clarity, the problem with your code is that unprivileged users can only seteuid in a few cases based on how the executable was invoked. So we need another solution.

This is an interesting problem. There are different ways you could solve it. I don't know if there is an accepted best-practice solution, but here are some options.

  1. Set sticky-group permissions on /var/cache/utility.

    This approach allows your utility to run under the initiators permissions. Make sure the user is in the group that owns /var/cache/utility, and change the permissions so that the group assignment is sticky for all contents. You can accomplish that with the following:

    mkdir /var/cache/utility
    chown -R :user /var/cache/utility
    chmod 2770 /var/cache/utility
    usermod -a -G users joe

    Now, since joe is in the users, when he runs your utility everything is ok. The group premission of any modified files in /var/cache/utility will remain users. The problem is that there is no group to which all users automatically belong. So this method won't automatically work for all users. There is also the security problem. You utility might modify files in /var/cache/utility in a well-behaved way, but this methods opens up the flood-gates to the wild west of userland.

  2. Split your utility into front- and back-ends.

    Dividing the utility into front- and back-ends is inconvenient, but does force you to formalise the operational interface. The communication between the parts can take two common forms:

    • Socket comms, whether unix sockets or TCP sockets. This requires that your back-end be a service.

    • Command-line tools. This is considerably simpler that using sockets, and your back-end does not run continuously.

    The idea is to uid-execute-sticky-bit on your back-end, so that it automatically runs under the owner's account, regardless of the current logged-in user. The front-end will still run under the credentials of the user.

    See if you can split your utility so that all manipulation of the cache is performed by the backend, but other activities are performed in the front-end. You can set the uid of the back-end as follows:

    chmod u+s /usr/bin/utility-back-end

    There is a reasonably good overview of this technique here. It is still somewhat inconvenient to partition the software like this, but it is the best solution I know. The following command will list all the utilities on your system that already use this method:

    find / -xdev \( -perm -4000 \) -type f -print0 | xargs -0 ls -l

Hope that helps.


UNIX home folder permissions - no access for other users

You could just change the permissions of your other (sensitive) subdirs with chmod 700 ~/sensitivedir.


Output who is currently logged in according to FILE. If FILE is not specified, use /var/run/utmp. /var/log/wtmp as FILE is common.


display this help and exit


output version information and exit


Copyright © 2012 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

reporting bugs

Report users bugs to bug-coreutils[:at:]gnu[:dot:]org
GNU coreutils home page: <>
General help using GNU software: <>
Report users translation bugs to <>

see also

The full documentation for users is maintained as a Texinfo manual. If the info and users programs are properly installed at your site, the command

info coreutils 'users invocation'

should give you access to the complete manual.


Written by Joseph Arceneaux and David MacKenzie.

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