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Monitoring your server with tmux

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There are lots of systems and utilities available to monitor your system. Many of these are web-based, or they run as a client-server system.

Unfortunately, there are several instances where the only allowed connection to the server of interest is over SSH. This might be for several reasons, the least of which being security. In these cases, you will likely still want some way of easily monitoring what is going on with your server. Using tmux, you can create a session which will run all of your monitoring software and
keep it running, regardless of whether you lose your connection or not.

This article will cover the basics of creating such a session, which you should be able to tune and tweak to fit your specific requirements. This way, you can simply log in using any available SSH connection and see, in an instant, all of the information that is of interest to you. Also, since you need to log into the system over SSH, you don’t need to worry about the problems of locking down other software, such as a web server.

server monitor
You can monitor a lot of processes and logs with tmux



Step by Step

Step 01

Getting tmux

Tmux originated as part of the OpenBSD system. It should be available in most distributions. For example, you can get it in Ubuntu with ‘sudo apt-get install tmux’. If you need the latest and greatest features, you can download the source code from SourceForge.

Step 02

Building tmux

The build system uses the usual ‘./configure; make; make install’ steps to build tmux. The reason you may want to build your own is that many distributions are behind one or more versions on the software provided by their respective repositories.

Step 03

Starting tmux

Starting tmux is as simple as typing ‘tmux’ and hitting Enter. Your console will clear for a split second, and then you will be presented with a Bash prompt again, along with a status bar located at the bottom of your screen. This status bar will contain information about your current tmux session.

Step 04

Starting top – CPU sorted

One of the things you will be interested in monitoring is which processes are using up the most CPU cycles on your server. A good tool for this is ‘top’. The default when you first start it is to sort processes based on CPU usage, so that is fine.

Step 05

Getting a new window

Here we come to one of the features of tmux; we need to create a new window in this tmux session. There are two ways to handle this: first, you can use the shortcut ‘C-b c’, or you can enter the complete command ‘new-window’. To enter commands, you need to enter ‘C-b :’ and then the command. This will put your current window into the background and open a new window in the foreground.

Step 06

Starting top – memory sorted

With a new window, you can start a new instance of top, sorting it on some other criteria. One of interest to most system administrators is which processes are using up memory. To sort the processes in this way, you will need to enter ‘M’. This may vary for other versions of top, so always check your version’s man page. You might also want to change the refresh rate by entering ‘d’ and setting the number seconds between each display.

Steo 07

Navigating windows

Now that you have multiple windows, you need to be able to navigate between them. The simplest way is to use the shortcut navigation keys. To move to a specific window, you can use ‘C-b’ and then the window number. Remember that window numbering starts at 0. If you simply want to move to the next or previous window, use ‘C-b n’ or ‘C-b p’.

Step 08

Creating new panes

The next great feature of tmux is the ability to break up windows into panes. This lets you have multiple programs running in the same window. To split the current pane horizontally, use ‘C-b %’ to get two panes, left and right. If you wish to split the current pane vertically, you would use ‘C-b “’.

Step 09

Navigating panes

Once you end up with multiple panes, you need to be able to navigate them. To move to the next pane in the current window, you would use the shortcut ‘C-b o’.

You can also rearrange panes within a window. To swap the current pane with the previous pane, use the ‘C-b {’ keyboard shortcut. To do so with the next pane, use ‘C-b }’.

Step 10

Using tail

Now that you have tmux essentials under your belt, it’s time to add some systems monitoring. You’ll want to monitor system logs, and you can do so in multiple panes, giving you an overall view. For example, navigate to an empty pane and enter:

tail -f /var/log/syslog

…in order to get a continually updating view of system messages.

Step 11

Following dmesg

Kernel messages can be followed by using the program dmesg. The problem is that it doesn’t do automatic refreshing. You can accomplish this with ‘watch -n 3 “dmesg | tail -n 15” ’, where the 3 is the number of seconds between refreshes, and the 15 is the number of lines to display.

Step 12

Network statistics

The next area you will want to monitor is networking. One utility you can use is netstat. To see all of the current connections on your server, you can use ‘netstat -at | grep -v LISTEN’. This is non-refreshing, so again you will likely want to pass it to watch in order to get an updating output.

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