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tmpdir in MySQL

shantanuo — Sat, 20 Jun 2009 01:52:21 GMT

In MySQL, the tmpdir path is mainly used for disk-based sorts (if the sort_buffer_size is not enough) and disk-based temp tables.

You can configure a slave with tmpdir=/dev/shm

Install SQLite

shantanuo — Wed, 13 May 2009 13:54:10 GMT

$ # As of March 2009, the latest version was 3.6.11.
$ wget www.sqlite.org
$ tar xzf sqlite-amalgamation-3.6.11.tar.gz
$ cd sqlite-3.6.11
$ ./configure && make
$ sudo make install

Using binlogs to update table

shantanuo — Mon, 11 May 2009 16:13:12 GMT

It is very interesting to know about how to extract statements from binlogs.

mysqlbinlog --start-datetime="`date +%Y-%m-%d' '%H:00:00 -d\"1 hour ago\"`" --stop-datetime="`date +%Y-%m-%d'
'%H:00:00`" mysql-bin.* | awk '/tbl_company/,/;/' | replace tbl_company mydb.tbl_company | mysql -h 172.29.0.0 -uroot -pPasswd mydb

I have not tested it, but guess it should work as expected.

awk power

shantanuo — Mon, 04 May 2009 14:37:12 GMT

$ cat salaries
Yvette van der Hoff 100000
Sarack Abama 400000
Bernie Madoff 0
John Q. Public 20000

$ awk '{print $NF, $0}' salaries | sort -nr -k1,1 | cut -d" " -f2-
Sarack Abama 400000
Yvette van der Hoff 100000
John Q. Public 20000
Bernie Madoff 0

$ awk -F '\t' -v 'OFS=\t' '{print $4, $3, $5, $2, $1}' data.txt
POP. COUNTY GOVT. CITY STATE
123 Gila Mayor Ely AZ
345 Lolo Sheriff Alma CA
22 El Paso Bubba Leroy TX

skip networking in MySQL

shantanuo — Sun, 03 May 2009 15:34:24 GMT

When there is maintenance work to be carried on the database server, you can simply skip networking so that no connection from any other server from the network will be accepted.
Simply enter the following in /etc/my.cnf:

[mysqld]
# Prevent network access to MySQL.
skip-networking

Saving data to text file

shantanuo — Sat, 02 May 2009 15:01:35 GMT

sqlite> .mode list
sqlite> .separator |
sqlite> .output test_file_1.txt
sqlite> select * from tbl1;
sqlite> .exit
$ cat test_file_1.txt
hello|10
goodbye|20
$

Silent mode in Linux

shantanuo — Thu, 30 Apr 2009 07:21:05 GMT

Sick of your computer speaker beeping like a demented Morse code machine whenever you type something wrongly? Teach it the sound of silence: run the command
setterm -blength 0
to mute the alarm bell no matter what kind of terminal you're typing into.
If you want it to happen every time you start a terminal, just add the command to your .bash_profile file.

valid date

shantanuo — Mon, 13 Apr 2009 10:14:50 GMT

validdate.sh script will look like this...

#!/bin/sh
userdate=$1
date -d $userdate &> /dev/null
if [ $? -ne 0 ] ; then
echo You entered an invalid date, $userdate
else
echo The date $userdate is valid
fi

# sh validdate.sh 2009-33-44
You entered an invalid date, 2009-33-44

IP addresses from access log

shantanuo — Tue, 07 Apr 2009 06:34:19 GMT

generate a list of IP address along with the number of times each was encountered and sort

cat access_log | awk '{print $1}' | sort | uniq -c | sort -nr

Backup a directory

shantanuo — Mon, 06 Apr 2009 10:17:47 GMT

#!/bin/sh
tar czvf $1.$(date +%Y%m%d-%H%M%S).tgz $1
exit $?

The arc script accepts a single file or directory name as a parameter and creates a compressed archive file with the current date embedded into the resulting archive file's name.

Time Zone error on slave

shantanuo — Mon, 30 Mar 2009 07:35:01 GMT

Last_Error: Error 'Unknown or incorrect time zone: 'Etc/UTC'' on query. Default database: 'db_name'. Query: 'INSERT INTO table SET column = CONVERT_TZ('2009-01-24', '-8:00', '+00:00')'

It’s a simple fix. Exit out of MySQL and run the following command - this works on Redhat, I’ve not tried it on other flavors.

shell> mysql_tzinfo_to_sql /usr/share/zoneinfo|mysql -u root -p

pager to md5sum

shantanuo — Mon, 30 Mar 2009 07:33:36 GMT

When optimizing queries by rewriting them to different forms that should return the same results, you can verify that you get the same results by taking a checksum of them.

Just set your pager to md5sum:

mysql> pager md5sum -
PAGER set to 'md5sum -'
mysql> select * from test;
a09bc56ac9aa0cbcc659c3d566c2c7e4 -
4096 rows in set (0.00 sec)

setting at jobs

shantanuo — Fri, 13 Mar 2009 04:37:25 GMT

# at -v 03:00 -f /root/shantanu/testat.sh > /root/shantanu/testat_result.txt 2>&1
# atq
7 2009-03-14 03:00 a root

better code

shantanuo — Tue, 10 Mar 2009 12:45:27 GMT

`test -s /var/log/mailme.txt`
if [[ $? -eq 0 ]] ; then
The above 2 lines can be written in one line as shown below:

if [[ -z /var/log/mailme.txt ]]; then

read .csv file

shantanuo — Tue, 10 Mar 2009 12:33:29 GMT

#!/bin/sh
awk -F"," '{print $1,$2}' read1.txt | while read var1 var2
do
echo $var1 $var2
done

common crontab entry

shantanuo — Tue, 10 Mar 2009 04:50:41 GMT

30 0 * * * updatedb > /dev/null 2>&1

# Clock synchronization
30 10 * * * CTIPDGT=`/sbin/ifconfig | grep -m 1 "inet addr" | grep -o "17.2.[0,8,26,32,40,56,16,40,56].*" | cut -d "." -f3`; /usr/sbin/ntpdate -u 172.29.${CTIPDGT}.123; /sbin/hwclock --systohc > /dev/null 2>&1

Declare your assets!

shantanuo — Sun, 01 Mar 2009 13:18:14 GMT

The declare command can be helpful in identifying variables, environmental or otherwise. This can be especially useful with arrays.

bash$ declare | grep HOME
/home/bozo

bash$ zzy=68
bash$ declare | grep zzy
zzy=68

bash$ Colors=([0]="purple" [1]="reddish-orange" [2]="light green")
bash$ echo ${Colors[@]}
purple reddish-orange light green
bash$ declare | grep Colors
Colors=([0]="purple" [1]="reddish-orange" [2]="light green")

Innodb troubleshooting

shantanuo — Thu, 26 Feb 2009 07:29:40 GMT

When you have your mysql up and running, just connect to any database (like mysql or test) and perform a following command:

CREATE TABLE innodb_table_monitor(x int) engine=innodb;

This will force innodb engine to start table monitor and dump some useful data regarding your tablespaces in mysql's error log

Watch replication

shantanuo — Wed, 25 Feb 2009 13:00:42 GMT

$ watch --interval=1 --differences 'mysql -uuser -ppassword -e "show slave status\G"'

findtable shell script

shantanuo — Thu, 05 Feb 2009 12:01:15 GMT

# vi /bin/findtable

#!bin/sh

mysql -e"select TABLE_SCHEMA, TABLE_NAME, ENGINE, TABLE_ROWS, CREATE_TIME FROM information_schema.TABLES where TABLE_NAME LIKE '%$1%';"

# chmod 777 /bin/findtable

# sh findtable test

processor info

shantanuo — Tue, 20 Jan 2009 14:14:19 GMT

Gather information about the processor. This is easily done as follows:

# cat /proc/cpuinfo

So, if I have purchased a dual processor quad-core server, I can run:

# cat /proc/cpuinfo | grep processor | wc -l

I would then expect to see 8 as the value. If I don't, I call up the vendor and tell them to send me another processor.

Help Me!

shantanuo — Fri, 02 Jan 2009 15:03:05 GMT

You can use the mysql client to perform lookups in the MySQL manual. This saves from having to keep a browser window open in order to look things up.
So how does it work?

mysql> help select;

mysql> help show

mysql> help contents

Show only PHP errors

shantanuo — Wed, 31 Dec 2008 11:16:02 GMT

Open /etc/php.ini file
# vi /etc/php.ini
Set error_reporting as follows:

error_reporting = E_COMPILE_ERROR|E_ERROR|E_CORE_ERROR

Alternately, you can show all errors, except for notices and coding standards warnings

error_reporting = E_ALL & ~E_NOTICE

Save and close the file. Restart apache web server:
# /etc/init.d/httpd restart

tinyurl.com

optimize all tables

shantanuo — Tue, 11 Nov 2008 11:44:04 GMT

mysql -e"SELECT CONCAT('OPTIMIZE TABLES ', GROUP_CONCAT(TABLE_SCHEMA, '.', TABLE_NAME ORDER BY TABLE_SCHEMA, TABLE_NAME SEPARATOR ',')) FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'dbname' GROUP BY TABLE_SCHEMA\G
" | awk -F: '{print $2}' | mysql

Unix cheatsheets

shantanuo — Sat, 08 Nov 2008 14:00:17 GMT

Cheat sheet act as a reference tool which provides cut and paste kind of commands to complete a specific task. I often recommend following set of best cheat sheets to students and IT professionals. It include Linux / UNIX command and shell scripting.

Read more: Top 10 Best Cheat Sheets and Tutorials for Linux / UNIX Commands