memcached-tool

Memcached : memcached-tool display/manage memcached server information


memcached-tool  localhost -h
Usage: memcached-tool [mode]

       memcached-tool 10.0.0.5:11211 display    # shows slabs
       memcached-tool 10.0.0.5:11211            # same.  (default is display)
       memcached-tool 10.0.0.5:11211 stats      # shows general stats
       memcached-tool 10.0.0.5:11211 dump       # dumps keys and values
       memcached-tool 10.0.0.5:11211 move 7 9   # takes 1MB slab from class #7
                                                # to class #9.

You can only move slabs around on a server that supports 'slabs reassign'
messages and only once slab memory is totally allocated, and only
once the target class is full.  (So you can't move from #6 to #9 and #7
to #9 at the same itme, since you'd have to wait for #9 to fill from
the first reassigned page)

Installing virtual box guest addition on ubuntu server

#apt-get install dkms 
#apt-get install build-essential
#apt-get install linux-headers-'uname-r'

reboot

#cd /mnt
#mkdir cdrom 
#mount /dev/cdrom /mnt/cdrom
#cd /mnt/cdrom
#./VBoxLinuxAddition.run 

file system performance : drop caches

#hdparm -tT /dev/sda
#hdparm -I /dev/sda

create test file on the disk
#dd if=/dev/zero of=/home/file.img bs=8k count=256

measuring performance
#iotop -b -n 1 -o
#cat /proc/slabinfo

Before start new test, restart system or clear disk caches
#sync; echo 3 > /proc/sys/vm/drop_caches
#sync; echo 0 > /proc/sys/vm/drop_caches


http://www.linuxinsight.com/proc_sys_vm_drop_caches.html

LiveCD software raid starting at md125

If you boot existing with live cd it may change the device name (/dev/mdx) starting from 125. This can prevent system from starting up normally.(/etc/fstab still use the old /dev/mdx name starting from md1). To rename software raid, stop and assemble it. :

This will rename md125 ... 127 to md1 ... md3 respectively

#mdadm --stop /dev/md125
#mdadm --assemble /dev/md1 /dev/sda1 /dev/sdb1
#mdadm --stop /dev/md126
#mdadm --assemble /dev/md2 /dev/sda2 /dev/sdb2
#mdadm --stop /dev/md127
#mdadm --assemble /dev/md3 /dev/sda3 /dev/sdb3

mysql user copy/migration

gensqluser.sh  : this script will gen sql statement for creating new user
---
mygrants()
{
  mysql -B -N $@ -e "SELECT DISTINCT CONCAT(
    'SHOW GRANTS FOR ''', user, '''@''', host, ''';'
    ) AS query FROM mysql.user" | \
  mysql $@ | \
  sed 's/\(GRANT .*\)/\1;/;s/^\(Grants for .*\)/## \1 ##/;/##/{x;p;x;}'
}

mygrants --host=localhost --user=username--password=password
---

host1# ./gensqluser.sh >> user.sql

host2# mysql -u -p < user.sql

bash script read file line by line

#/bin/bash

while read myline
do
  echo $myline
done < inputfile

awk basic

awk is very useful tool for linux user.
For example, you have output from ps aux like this :

#ps aux 

root      2213  0.0  0.4   6596  2428 pts/2    S    12:08   0:00 bash
root      2235  0.0  0.1   4848   952 pts/2    S+   12:08   0:00 /bin/bash xxx
root      2236  0.0  0.6   7132  3236 pts/2    S+   12:08   0:04 ssh xxx

The second column is PID, and 8th is process state.
To find the zombie process you just execute the following command  :

# ps aux | awk '{ print $8 " " $2 }' | grep -w Z


See just use $th of the column, you will get the value of that column. Also, you can apply even you have comma separated field with -F option.

For more usage of this command please consult
#man awk

:)