system administrator HowTo - Linux / Unix Q & A from nixCraft

FreeBSD Install sudo Command To Execute A Command As Root

last updated May 15, 2018 in FreeBSD, FreeBSD Jails (VPS), UNIX

I have recently started to managing FreeBSD server along with Ubuntu Linux. However, sudo command, always shows me the following error:

zsh: command not found: sudo

How do I solve this problem and use sudo under a FreeBSD 9.x/10.x/11.x system?

Howto: Shutdown Linux System From Terminal

last updated April 20, 2012 in Linux

How do I shutdown Linux system from terminal or command line options?

HowTO: Linux Disable a User Account Command

last updated December 1, 2012 in Linux

How do I disable a user account under Linux operating systems? How can I completely disable a user account Linux server?

Linux Change Password

last updated July 29, 2013 in BASH Shell, Commands, Linux

How do I change my own password as well as the passwords of other users as required under Linux operating system without using GUI systems? How can I change or set user password on Linux operating systems?

How To: Ubuntu / Debian Linux Regenerate OpenSSH Host Keys

last updated June 9, 2018 in Debian / Ubuntu, Linux, Networking, OpenBSD, Package Management, Ubuntu Linux

How do I regenerate OpenSSH sshd server host keys stored in /etc/ssh/ssh_host_* files? Can I safely regenerate ssh host keys using remote ssh session as my existing ssh connections shouldn’t be interrupted on Debian or Ubuntu Linux? How do I regenerate new ssh server keys? How to regenerate new host keys on a Debian or Ubuntu Linux?

Mac OS X Remove SSH Known Host

last updated December 15, 2009 in BASH Shell, Mac OS X

I‘ve reinstalled Linux on remote server and now trying to connect it over ssh using Mac OS X:

ssh user@server1.example.com

But I’m getting an error which read as follows:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
5c:9b:16:56:a6:cd:11:10:3a:cd:1b:a2:91:cd:e5:1c.
Please contact your system administrator.
Add correct host key in /Users/user/.ssh/known_hosts to get rid of this message.
Offending key in /Users/user/.ssh/known_hosts:1
RSA host key for server1.example.com has changed and you have requested strict checking.
Host key verification failed.

How do I fix this problem under Mac OS X?

File Size Limit Exceeded Error Under Linux and Solution

last updated September 2, 2013 in BASH Shell, Linux, PHP

I am trying to copy a file called act.dat. I do have enough disk space to copy this file. I am getting an error “file size limit exceeded” under Linux. How do I get rid of this error?