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Users & Groups Management HowTos

Learn all about users and groups on Linux and Unix like operating systems. Topic include user & group creations, permissions & ownership, access control, ACL, and more ( rss feed ).

Linux / UNIX: Create Username or Groups in UPPER Case

Q. How do I create username or user groups in upper case under Linux / *BSD / UNIX operating systems?
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Debian / Ubuntu Linux Public key Blacklisted (see ssh-vulnkey(1)) Error and Solution

Q. When ever I try to login to my remote Debian Linux server called in013.example.com, I get the following error message in /var/log/auth.log file:

Jul 1 17:04:36 in013 sshd[14447]: Public key 48:de:55:22:xx:yy:zz:yy:xx:yy:zz:yy::88:e8:87:47 blacklisted (see ssh-vulnkey(1))
Jul 1 17:04:36 in013 sshd[14447]: Public key 48:de:55:22:xx:yy:zz:yy:xx:yy:zz:yy::88:e8:87:47 blacklisted (see ssh-vulnkey(1))

I’m using Ubuntu Linux as desktop operating system. How do I fix this error?
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UNIX / Linux Command To Check Existing Groups and Users

How do I check the existing Linux / UNIX users and groups under Linux operating system?
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Linux Change Default User Home Directory While Adding A New User

By default base directory for the system user is set to /home directory. I’d like to add user to /iscsi/home/${user} directory instead of the default /home. How do I force useradd command to add user to /iscsi/home under CentOS / RHEL / Fedora Linux server?
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Linux sudo Configuration

Q. Can you tell me how to configure sudo to provide access to end users? How do I allow to run programs with the security privileges of another user using sudo?
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Remove Linux User From a Secondary Group ( Supplementary Groups )

Q. User tom is a member of a group called sales and printer. I’d like to remove tom from a group called printer without editing any user configuration text files stored at /etc/ directory?
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FreeBSD Install BASH Shell

I would like to Bash shell under FreeBSD for bash programming. How do I install bash shell under FreeBSD UNIX operating system?
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Stop Ubuntu / Debian Linux From Deleting /tmp Files on Boot

Q. I know /tmp as it named is a temporary dircory, Debian policy is to clean /tmp at boot. However, I’d like to configure my Ubuntu Server to stop deleting files from /tmp on boot due to custom configuration issue. How do I configure behavior of boot scripts to stop deleting files on boot?
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Linux 64 bit Server

Q. Can you tell me more about Linux 64-bit server distribution for production webhosting environment?
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Linux logged out a user automatically

Q. We have a few users who frequently forget to log out and I’d like to force them or automatically log out a user in case of inactivity detected. How do I force user to be logged out automatically?

A. BASH provides TMOUT variable. It is necessary for security reasons to have an inactive user logged out after a period of inactivity from Linux / UNIX ssh / telnet session. This can be accomplished by setting an environment variable TMOUT.

Automatically log out a user

Add the TMOUT variable to your /etc/bashrc file:
# vi /etc/bashrc
Set TMOUT to 300 seconds (5 minuets):
TMOUT=300
Save an close the file. Above config would automatically logout users after 300 seconds of inactivity. Please note that this hack only works with run level 2, 3 i.e. it will not work with GUI sessions.