While monitoring a http/php server, I needed to do some statistics about php-cgi memory usage.

Playing with memory_limit in PHP, we wanted to know the average memory usage per php-cgi process. This is easily calculated with our best friend awk.

First, get the number of php running processes:

# ps aux | grep php-cgi | grep -v grep | wc -l
126

Then, use awk to calculate the average memory usage for these processes:

# ps aux | grep --exclude=grep php-cgi | grep -v grep | awk 'BEGIN{s=0;}{s=s+$6;}END{print s/126;}'
33987.8

The number used in the calculation is the field RSS given by ps. The ps manual page says:

rss: resident set size, the non-swapped physical memory that a task has used (in kiloBytes)

You can also calculate the total memory used by all php-cgi processes:

# ps aux | grep --exclude=grep php-cgi | grep -v grep | awk 'BEGIN{s=0;}{s=s+$6;}END{print s;}'
4302028

If you need to watch the trend of this average memory usage, a little shell loop does the trick:

# while [ 1 ]; do ps aux | grep --exclude=grep php-cgi | grep -v grep | awk 'BEGIN{s=0;}{s=s+$6;}END{print s/126;}'; sleep 2; done
34401.3
34405.1
34408.4
34409.4
34414.2
34417

The dmidecode command gives you all informations available about your memory.

With the special parameter “-t 16″, you can see the maximum (physical) memory that your server can have:

$ dmidecode -t 16
# dmidecode 2.8
SMBIOS 2.4 present.

Handle 0x1000, DMI type 16, 15 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: Multi-bit ECC
Maximum Capacity: 32 GB
Error Information Handle: Not Provided
Number Of Devices: 8

Here we can see that your server can handle up to 32Gb

Check empty memory slots

To know which slots are used or not use the “-t 17″ flag.

dmidecode -t 17 | grep Size
        Size: 2048 MB
        Size: 2048 MB
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed
        Size: No Module Installed

Links

• DMI specification
• SMBIOS specification