Geekdom

Linux systemd can be your friend

Rich — Wed, 16 May 2012 20:15:39 +0000

systemd messes with your mind. Definitely. The easy management of /etc/init.d/ files or /etc/rc.d files is easy to grasp; easy to get the mind around a simple ordering of complex events. Replace that with systemd, and the brain wants to revolt.

But there are some upsides to this trend. systemd is smart. It can do a lot in parallel. Yes, ‘systemctl enable myapp.service’ is a heck of a lot to type. Yet, systemd gives you features like:

systemd-analyze blame

systemctl –order

and, one of the really cool ones:

systemd-analyze plot > plot.svg && eog plot.svg

What is this “notty” host?

Rich — Tue, 15 May 2012 17:06:49 +0000

In looking at the process listing on a linux server, an administrator may see a process listed as “sshd: root@notty”. An administrator, even a seasoned one, may immediately wonder “what is this ‘notty’ host?” and start down the path of trying to determine what host that is.

However, sit back and take a deep breath: “notty” means “NO TTY”. In other words, there is no TTY associated to the process, which means that the process was initiated remotely. In this case, a non-interactive process was initiated remotely over SSH.

How To Clear / Remove the GUID Partition Table (GPT) from a drive

Rich — Sat, 12 May 2012 17:16:43 +0000

If a drives has a GPT (GUID Parition Table) on it, Windows 7 and Linux will happily use it. HOWEVER, all of the add-on tools to format a partition on that drive as fat32 (for those that are using large drives) do not understand that partition table type.

To clear the GPT entirely from a linux machine:

 parted /dev/sdc
 mklabel msdos
 quit

How to Find Out Who or What is Listening on that Port (linux)

Rich — Mon, 23 Apr 2012 16:38:07 +0000

This comes up every now and then, and it is one of those commands that is hard to remember. There are a number of ways to do this, but this one is easy. It has to be run by root, though.

netstat -lnptu | grep theportnumber

Limiting access via SSH

Rich — Wed, 18 Apr 2012 19:55:47 +0000

Generally, it is a bad idea to allow regular users on a linux server. OpenSSH provides directives to control who does and does not have access via ssh:

AllowUsers
AllowGroups
DenyUsers
DenyGroups

Any one of those directives can be used. AllowUsers and AllowGroups is defined as “allow only the users or the users of the listed groups to have access to the system”. DenyUsers and DenyGroups is defined as “allow all users except those listed or allow all users except those who are in the listed groups”.