Synergy – Cross Platform Mouse and Keyboard Sharing

SynergyTim Haroutunian recently discovered the open-source, cross-platform utility Synergy which allows you to seamlessly share a keyboard and mouse with several computers of varying platforms.

The behavior of Synergy is similar to having multiple monitors on a single computer with the added advantage that you’re controlling multiple systems. Since I have both a Mac OSX desktop and a Windows laptop on my desk it was nice to reduce myself to one keyboard and mouse! Even clipboard data is shared between the systems.

Setup was a little less than intuitive but well worth it. Out of the box, security is fairly weak, however the Synergy project page does have instructions on how to tunnel Synergy traffic through SSH. Mac, Windows and Linux binaries are available along with the source code for those DIYers.

kvm, cross-platform, software, systems administration, linux, OSX

SSH Without A Password

Zach has posted a good quick reference for setting up SSH to use a shared key for authentication instead of a password on a UNIX system. It’s important to keep your keys secure, but this can allow you to set up scripts to execute commands or move files between multiple hosts without prompting for passwords.

If memory serves this type of authentication is enabled by default on most ssh servers, but if it doesn’t work talk to your sys-admin to see if it is disabled.

unix, linux, solaris, mac osx, osx, ssh, security

UNIX Find And Execute

Zach tells me I need to post how to find files and execute a command on those files. While the man pages are always the definitive reference, these are the options I use frequently. As usual, anything in italics should be replaced with the details for your search.

Note: WordPress loves to convert quotes into fancy quotes (pointing in from each side) so these commands may not work too well if copied and pasted. On the bright side, there’s no time like the present to start commiting these to muscle memory.

Find a file and execute a specific command:

find path conditions -exec command {} \;

find ./ -name "*.php" -exec cat {} \;

The open/close curly bracket marks where the name of each file found will be substituted and the backslash-semicolon marks the end of the command to execute.

Here are a few other options I use frequently:

Search for a file by name:

find path -name filename

find ./ -name style.css

Search by name with wildcards:

find path -name "filename"

find ./ -name "*.html"

Search for files modified within the past n days:

find path -mtime -n

find ./ -mtime -7

Search for files modified before the past n days:

find path -mtime +n

find /tmp -mtime +3

These are mostly based on my experience in Solaris using the bash shell. They should work just about everywhere, but check the man pages as mileage will vary.

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unix, solaris, linux, mac osx, osx, sysadmin, systems administration

UNIX Load Averages Explained

If you’ve spent much time working in a UNIX environment you’ve probably seen the load averages more than a few times.

load averages: 2.43, 2.96, 3.41

I have to admit that even in my sysadmin days I didn’t fully understand what these numbers were, but Zach did some digging a while ago to try to understand where these numbers are comming from.

In his blog entry from late last year, Zach sums it up quite nicely:

In short it is the average sum of the number of processes waiting in the run-queue plus the number currently executing over 1, 5, and 15 minute time periods.

The formula is a bit more complicated than that, but this serves well as a functional definition. Zach provides a bit more detail in his article and also points out Dr. Neil Gunther’s article on the topic which has as much depth on the topic as anyone could ever ask.

So what does this mean about your system?

Well, for a quick example let’s consider the output below. The load average of a system can typically be found by running top or uptime and users typically don’t need any special privileges for these commands.

load averages: 2.43, 2.96, 3.41

Here we see the one minute load average is 2.43, five minute is 2.96, and fifteen minute load average is 3.41.

Here are some conclusions we can draw from this.

  • On average, over the past one minute there have been 2.43 processes running or waiting for a resource
  • Overall the load is on a down-trend since the average number of processes running or waiting in the past minute (2.43) is lower than the average running or waiting over the past 5 minutes (2.96) and 15 minutes (3.41)
  • This system is busy, but we cannot conclude how busy solely from load averages.

It is important here to mention that the load average does not take into account the number of processes. Another critical detail is that processes could be waiting for any number of things including CPU, disk, or network.

So what we do know is that a system that has a load average significantly higher than the number of CPUs is probably pretty busy, or bogged down by some bottleneck. Conversely a system which has a load average significantly lower than the number of CPUs is probably doing just fine.

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UNIX, systems administration, sysadmin, solaris, linux, load averages, system monitoring, sun, mac, osx