cli

Had an ulimit problem

I’m optimizing some scripts that split our apache logs each night. I gotta admit Apache’s ‘split-logfile’ script written in perl is a LOT faster than doing it via f.example bash . But splitting up a log file with more than 2000 vhosts resluted in the script crashing. I had to up my ‘open files’ limit with :

# ulimit -n 4096
# 

http://www.debian.org/doc/manuals/securing-debian-howto/ch4.en.html
http://httpd.apache.org/docs/2.0/programs/other.html

Testing read/write speed of disks

Upon testing the performance of a raid 6 array with 13 disks i wanted to check read/write performance, an easy way to do this fast on Linux (Debian) is simply using ‘time’ and ‘dd’:

bakis:/var/raid6volume# time dd if=/dev/zero of=./testingtransfer bs=16k count=16k
16384+0 records in
16384+0 records out
268435456 bytes (268 MB) copied, 1.48474 s, 181 MB/s

real	0m1.513s
user	0m0.008s
sys	0m1.456s
bakis:/var/raid6volume# time dd if=./testingtransfer of=/dev/null bs=16k
16384+0 records in
16384+0 records out
268435456 bytes (268 MB) copied, 0.156663 s, 1.7 GB/s

real	0m0.159s
user	0m0.004s
sys	0m0.160s
bakis:/var/raid6volume#

The ‘read’ test above isn’t real since the file has been cached . But a rsync is working in the background so I couldn’t umount /var/raid6volume for this example.

Initially I was doing this to test performance over nfs for the same array, one has to umount / mount the share between each test to make sure nothings in the cache.

Working with nfs, tuning wsize and rsize on the client side also gives a lot better performance (at least in my case), see the link bellow for more info.

I got these hints from debianhelp.co.uk

How much ram in my graphics card ?

Nice command to find how much ram my graphics card has. Use ‘lspci’ to get the pci id and throw it back to lspci like this:

joar@juno:~$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 09)
joar@juno:~$ lspci -v -s 00:02.0
00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 09)
	Subsystem: Lenovo Device 3a02
	Flags: bus master, fast devsel, latency 0, IRQ 30
	Memory at f4000000 (64-bit, non-prefetchable) [size=4M]
	Memory at d0000000 (64-bit, prefetchable) [size=256M]
	I/O ports at 1800 [size=8]
	Capabilities: <access denied>
	Kernel driver in use: i915
	Kernel modules: i915

joar@juno:~$