The top command allows you to view system tasks running in real-time. It provides a good summary of your system to quickly check if anything stands out that may be causing issues with your website or server. View the following man page for further details:
How do I run the 'top' command?
You must log into your server via SSH in order to run the top command. View the following articles for information on how to set up a Shell user and log into your server:
top has a few shortcut keys that are available which changes how the information is displayed:
|# Shortcut Key||Description|
|c||Toggles the COMMAND column between showing the command or program name.|
|t||Displays summary information on and off.|
|m||Displays memory information on and off.|
|A||Sorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on the system.|
|f||Enters an interactive configuration screen for top. Helpful for setting up top for a specific task.|
|o||Enables you to interactively select the ordering within top.|
|r||Issues renice command.|
|k||Issues kill command.|
|z||Turns color/mono on and off.|
This is the first step. Many times you can tell which site is causing trouble by simply checking your active processes. Log into your server via SSH and take a look at which processes are running. Let's say you see something like this:
[server]$ top -c top - 14:37:35 up 10 days, 17:35, 3 users, load average: 0.83, 0.89, 1.11 Tasks: 16 total, 1 running, 15 sleeping, 0 stopped, 0 zombie Cpu(s): 34.7%us, 4.8%sy, 1.7%ni, 56.5%id, 0.9%wa, 0.2%hi, 1.1%si, 0.0%st Mem: 32966092k total, 32546460k used, 419632k free, 6369232k buffers Swap: 8000328k total, 228972k used, 7771356k free, 12650516k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 8384 username 20 0 66984 11m 6852 S 1 0.0 0:03.62 php5.cgi 8385 username 20 0 66044 10m 6700 S 0 0.0 0:00.24 php5.cgi 10895 username 20 0 65940 10m 6848 S 0 0.0 0:00.92 php5.cgi 10917 username 20 0 65980 10m 6848 S 0 0.0 0:00.79 php5.cgi 7542 username 20 0 65956 10m 6860 S 0 0.0 0:00.51 php5.cgi 7818 username 20 0 65980 10m 6860 S 0 0.0 0:00.35 php5.cgi 7828 username 20 0 65988 10m 6860 S 0 0.0 0:00.33 php5.cgi 7917 username 20 0 66016 10m 6860 S 0 0.0 0:00.43 php5.cgi 8152 username 20 0 65976 10m 6856 S 0 0.0 0:04.21 php5.cgi 8380 username 20 0 65932 10m 6848 S 0 0.0 0:04.03 php5.cgi 8386 username 20 0 66020 10m 6860 S 0 0.0 0:00.32 php5.cgi 10896 username 20 0 65908 10m 6848 S 0 0.0 0:00.66 php5.cgi 10919 username 20 0 65948 10m 6848 S 0 0.0 0:00.24 php5.cgi
If it looks something like the above, then you're very likely running into this problem. Generally, if you're running more than 10 PHP processes at once and they hold pretty steady, then this is an indication of memory issues.
This may help you diagnose a problem on a single site under your username, but if you have more than one site you should run lsof to find any open files that could potentially be causing an issue.
Sort results by memory usage
You can sort the results of top by memory usage. First, run the top command to view the live results.
Once opened, press Shift + m and the output is sorted by memory usage.
Displaying memory usage of a specific process
[server]$ top -b -n 1 | grep -i [EnterProcessName]
VPS and Dedicated servers
If you're on a VPS or Dedicated server, running top will display a lot of system processes run by users like 'root', 'dhapache', 'postfix', and so on. If you want to see only the processes running from a specific user, use the following command:
[server]$ top -U [EnterUsername]