Shantanu's Blog
Database ConsultantDecember 31, 2009
Conquer the Konqueror
Everything starts with "K" like "kusum", "Kaun banega Karodpati", "Saas bhi kabhi bahu thi" etc. My favorite is "KDE ka Konqueror" in which K. Kapoor can "fish" for files from another server and simply right click to Kopy.
Here is how:
1) Start Konqueror
# konqueror &
2) Use Ctrl + tab to start a new tab
3) Use fish protocol to connect to ssh sever.
fish://111.222.333.444
You can connect to ftp server using the ftp protocol.
ftp://ftp.saraswaticlasses.net
4) Now navigate to the folder and then right click on the file to copy, paste it anywhere.
Labels: linux tips
Backup Cron
58 13 * * * /usr/bin/mysqldump -uroot -pPassWord --compact --databases db1 db2 db3 db4 |
zip > /home/develop/backup/central_mydt$(date +'\%d\%m\%y').zip
2>> /home/develop/backup/central_err.txt
After unzipping the file there will a file with the name -
You have to rename it to be more useful
mv \- somefile.txt
Labels: mysql tips
December 29, 2009
Read binary files
But you can also use show binlog events to read the binary file as shown below:
mysql> system ls /var/log/mysql/ -lh
total 76M
-rw-rw---- 1 root root 15K Dec 26 14:07 mysql-bin.000001
-rw-rw---- 1 root root 575K Dec 26 14:07 mysql-bin.000002
-rw-rw---- 1 root root 254 Dec 26 14:07 mysql-bin.000003
-rw-rw---- 1 root root 54M Dec 26 22:00 mysql-bin.000004
-rw-rw---- 1 root root 1.9K Dec 27 15:43 mysql-bin.000005
-rw-rw---- 1 root root 117 Dec 27 16:15 mysql-bin.000006
-rw-rw---- 1 root root 22M Dec 29 19:40 mysql-bin.000007
-rw-rw---- 1 root root 224 Dec 28 11:31 mysql-bin.index
-rw-r----- 1 root mysql 4.5K Dec 29 19:43 mysqld.log
-rw-rw---- 1 root root 3.5K Dec 28 14:28 mysql-slow.log
mysql> show binlog events in 'mysql-bin.000007' from 4 limit 10;
| mysql-bin.000007 | 928 | Query | 99 | 407 | use `umr`; insert into master values("55063","A","JC","umrd","ok","P","Tambarbge","OnService","6163899","Naur","1974-11-04","Mr","NAUR","NGP","UMR","UMRD") |
| mysql-bin.000007 | 1335 | Xid | 99 | 1362 | COMMIT /* xid=488 */
Labels: mysql tips
December 28, 2009
lsof - list open files
lsof
# lists all the processes, which are using the file in some way.
lsof /path/to/file
# This will list all the files that are open by users rms and root.
lsof -u root
# Find all open files by program’s name.
lsof -c apache
# print all open files by all users who are not root.
lsof -u ^root
# List all open files by the process with PID.
lsof -p 1
lsof -p 450,980,333
# List all network connections.
lsof -i
# List all TCP network connections.
lsof -i tcp
# Find who’s using a port.
# The :25 option to -i makes lsof find processes using TCP or UDP port 25.
lsof -i :25
# to find who’s using a TCP port, use:
lsof -i tcp:80
# Find all network activity by user.
# Here the -a option combines -u and -i to produce listing of network file usage by user hacker.
lsof -a -u hacker -i
# List all NFS (Network File System) files.
lsof -N
# List all files associated with specific file descriptors.
# This lists all files that have been opened as file descriptor 2.
lsof -d 2
# txt for programs loaded in memory and executing:
lsof -d txt
# Output PIDs of processes using some resource.
lsof -t -i
# The -t option outputs only PIDs of processes. Used together with -i it outputs PIDs of all processes with network connections. It’s easy to kill all processes that use network:
kill -9 `lsof -t -i`
Labels: linux tips
InnoDB setting
innodb_data_file_path=ibdata1:2000M:autoextend #(default: 10M)
#50-80% of memory is a safe bet. I set it to 12G on 16GB box
innodb_buffer_pool_size=12G #(default: 8 MB)
innodb_additional_mem_pool_size=100M
innodb_log_file_size=256M #(default: 5 MB)
innodb_log_buffer_size=8M #(default: 1 MB)
innodb_flush_log_at_trx_commit=2
Labels: mysql tips
December 18, 2009
Finding PHP syntax errors
If all your .php files are in /var/www/html then you can type the following command.
# find /var/www/html -name '*.php' -exec php -l {} \; | grep -v '^No syntax'
You can save the output to a text file by appending "> tofile.txt" at the end of the above command.
The output will look something like this...
Parse error: syntax error, unexpected '<' in ./reports/extra/rc7bkp2.php on line 265
Errors parsing ./reports/extra/rc7bkp2.php
Parse error: syntax error, unexpected $end in ./reports/extra/rc6bkp.php on line 525
Errors parsing ./reports/extra/rc6bkp.php
Parse error: syntax error, unexpected '}' in ./login/login.php on line 53
Errors parsing ./login/login.php
Parse error: syntax error, unexpected $end in ./commom/bkp/25_nov/Process1.php on line 93
Errors parsing ./commom/bkp/25_nov/Process1.php
_____
If you want to check if a file for e.g. reserve.php has any errors, use the following command....
$ tail -f /var/log/httpd/error_log | grep 'reserve.php'
[Fri Dec 18 16:46:30 2009] [error] [client 59.95.20.15] PHP Notice: Undefined index: ucd in /var/www/html/login.php on line 531, referer: http://111.222.333.444/reserve.php
[Fri Dec 18 16:46:33 2009] [error] [client 117.195.35.82] PHP Notice: A session had already been started - ignoring session_start() in /var/www/html/checkPass.php on line 2, referer: http://666.777.888.999/reserve.php
Labels: php tips
December 16, 2009
Issues with SELinux firewall
lokkit
But this will almost surely stop mysql from starting on the next boot if you have changed the datadir path. You will get an error something like this...
091216 23:51:41 mysqld started
091216 23:51:42 [Warning] Can't create test file /mysql/localhost.lower-test
091216 23:51:42 [Warning] Can't create test file /mysql/localhost.lower-test
/usr/libexec/mysqld: Can't change dir to '/mysql/' (Errcode: 13)
091216 23:51:42 [ERROR] Aborting
091216 23:51:42 [Note] /usr/libexec/mysqld: Shutdown complete
091216 23:51:42 mysqld ended
You can either disable it by using the same command again. If you want to use SELinux and still start mysql from a different location, use the following tip:
If you start 'system-config-securitylevel' (RHEL/CentOS) in a graphical environment and click on the SELinux tab, then right down at the bottom of the 'Modify SELinux Policy' section there is a menu item 'SELinux Service Protection'. Expand this and one of the items is 'Disable SELinux protection for mysqld daemon'. Check the box next to this and click 'OK'.
/usr/sbin/setenforce 0
The above will disable selinux.
But you need to either specify the appropriate setenforce parameter in /etc/sysconfig/selinux or pass the parameter selinux=0 to the kernel, either in /etc/grub.conf or at boot time.
Labels: mysql tips
December 13, 2009
Using PHP to avoid filesort
Such queries are very slow and hence PHP needs to be used.
mysql> explain SELECT * FROM ABCD WHERE a=1 AND b=1 ORDER BY c DESC, d ASC\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: ABCD
type: ref
possible_keys: PRIMARY
key: PRIMARY
key_len: 8
ref: const,const
rows: 2
Extra: Using where; Using index; Using filesort
1 row in set (0.00 sec)
So, we changed 1 query into 11 queries (10 parents per page) to make the page load happen faster, by getting rid of the filesort.
FOREACH($C_parent as $i => $c_id) {
$C_parent[$i] = SELECT SQL_CALC_FOUND_ROWS * FROM ABCD WHERE A=? AND B=? AND C=$c_id ORDER BY D ASC LIMIT 1;
}
Calculating the running total is another example where we need to use PHP as writing complex query is time consuming as well as very slow.
PHP at command prompt
# php -c /etc/php.ini /var/www/html/TablesList.php
Warning: mysql_pconnect(): Access denied for user 'sink'@'localhost' (using password: YES) in /var/www/html/dbconnect.php on line 6
Error Occurred while communicating with the database!
2) Check Syntax error
# php -l /var/www/html/TablesList.php
No syntax errors detected in /var/www/html/TablesList.php
3) Strip the source code of comments and whitespace
# php –w example.php
Can be useful if you need to reduce the file size.
4) Run php code from the command line
# php -r "$foo = 'hello!'; $foo = strtoupper($foo); echo $foo;"
Directly run php code from the command line without using the php start and end tags.
Labels: php, shell script
December 06, 2009
UNIX case study - 22
#!/bin/sh
set -x
for i in "yahoo.com" "facebook.com" "google.com" "reddit.com" "cnet.com" "bbc.co.uk"
do
for j in "4.2.2.2" "8.8.8.8" "208.67.222.222"
do
echo $j $i `dig @$j $i | grep Query | awk -F ":" '{print $2}'`
done
done
Labels: linux tips, unix case study
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