So you inherit a box running linux and you have no idea which flavor of linux it is. How do you find out?

If all you need the kernel version you can try
uname -a

This outputs something like this

Linux localhost.localdomain 2.4.20-31.9 #1 Tue Apr 13 18:04:23 EDT 2004 i686 i686 i386 GNU/Linux

If you need the actual distro name you can try
cat /etc/*release

In Ubuntu it shows up as

DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=9.04
DISTRIB_CODENAME=jaunty
DISTRIB_DESCRIPTION=”Ubuntu 9.04″

Or even
cat /etc/issue

which spits out the following on Ubuntu

Ubuntu 9.04 \n \l

You can combine all three to get the following
uname -a && cat /etc/*release && cat /etc/issue

Update:
Another one to add to the list
cat /proc/version

 

By default CentOS allows ssh access to all users who can authenticate with the server. This can be a security risk especially when you have setup the server to authenticate against an Active Directory domain. In this case all the users on the domain can login via ssh to your CentOS server. You can, however, very easily restrict logins to specific users, computers, or even users on specific computers.

To do this, edit /etc/ssh/sshd_config by adding the AllowUsers directive in the following format.

AllowUsers user@host

This allows the user ‘user’ to login at the host named ‘host’. Multiple users can listed by separating each with a space. You can also use * to specify wildcards. You can also specify IP addresses and ranges using *.

AllowUsers *@192.168.1.* johndoe@192.168.1.3

This will allow all users to log into all computers with address starting with 192.168.1 and the user johndoe to log only into the with IP address 192.168.1.3.

This will work for other Linux OSes as well.

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