Both InnoDB and PostgreSQL - as well as many other databases - use a technique called multi-version concurrency control (MVCC) to provide transaction isolation: transactions should not see the work of other, uncommitted transactions. MVCC means that, when a row is updated, the database stores both the old and new versions of the row.


Monday, May 21, 2012


  1. rkhunter --check --rwo --summary > /tmp/rkhunter_final.log
  2. cat /tmp/archival_system/delJS_downtime.log | grep "^[0-9]" | awk '{sum=sum+$1} END{print sum}'
  3. grep "proxy\:" /var/log/apache_front_error_log | awk '{print $NF}' |grep -v resid | sort | uniq -c | sort -n
  4. for i in `ls -lrt | awk '{print $7"\t"$9}' | grep ^31 | awk '{print $2}'`; do cat $i  | tai64nlocal | grep "m.jannath\_perthous100\@yahoo.com"; cat $i  | tai64nlocal | grep "mahesh_f_b@yahoo.co.in"; cat $i  | tai64nlocal | grep "annaisai1986@yahoo.co.in"; cat $i  | tai64nlocal | grep "anfaz_m@hotmail.com"; cat $i  | tai64nlocal | grep "sujitha2012@gmail.com"; cat $i  | tai64nlocal | grep "desiginer@gmail.com"; done
  5.  for i in `ls -lrt | awk '{print $7"\t"$9}' | grep ^31 | awk '{print $2}'`; do cat $i  | tai64nlocal | grep "m.jannath\_perthous100\@yahoo
  6. cat /tmp/list | awk '{print $5}' | xargs -i egrep "adityaseth09@gmail.com|kvenk111@yahoo.co.in|knvs.prasad@gmail.com" /home/qmail-logs/2010/{}
  7. ls -ltra | awk '{print $5," ",$9}' | awk '$1 < 3000' | awk '/gif|png|jpg/ {print $2}' | xargs -I % cp -rp % /web/R/images/ 
  8. to massively clean lines containing x’s in front some css declarations in a group of files                          ls | awk '/.css$/' | xargs sed -i.bk -e '/^ *x.*$/d'    next...            find . -type f -exec grep -i '^ *x' /dev/null {} + | awk '!/svn|htdocs/' | cut -c 3- | awk '!/^#/' | awk -F ':' '{print $1}' | awk '/.css$/'| xargs sed -i.bk -e '/^ *x.*$/d\'
  9. seq -w 1 30 | xargs -i -t zcat in_Feb2011/in_Employer-{}Feb2011.gz | egrep 'resume.html?resid=3304847|resume.html?resid=30780899|resume.html?resid=31313778|resume.html?resid=31628106'

sar - Collect, report, or save system activity information.
      -b :Report I/O and transfer rate statistics.
      -B :Report paging statistics
      -d :Report activity for each block device (kernels 2.4 and newer only)
      -q :Report queue length and load averages
      -r :Report memory and swap space utilization statistics
      -u :Report CPU utilization.

iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.
       -d : device utilization report
       -c : CPU usage report
       -x : Display  extended  statistics

    * rrqm/s : The number of read requests merged per second that were queued to the hard disk
    * wrqm/s : The number of write requests merged per second that were queued to the hard disk
    * r/s : The number of read requests per second
    * w/s : The number of write requests per second
    * rsec/s : The number of sectors read from the hard disk per second
    * wsec/s : The number of sectors written to the hard disk per second
    * avgrq-sz : The average size (in sectors) of the requests that were issued to the device.
    * avgqu-sz : The average queue length of the requests that were issued to the device
    * await : The average time (in milliseconds) for I/O requests issued to the device to be served. This includes the time spent by the requests in queue and the time spent servicing them.
    * svctm : The average service time (in milliseconds) for I/O requests that were issued to the device
    * %util : Percentage of CPU time during which I/O requests were issued to the device (bandwidth utilization for the device). Device saturation occurs when this value is close to 100%.

Device:     rrqm/s     wrqm/s     r/s     w/s     rsec/s       wsec/s     rkB/s         wkB/s         avgrq-sz     avgqu-sz     await     svctm     %util
cciss/c0d0     2269.60 132.60     296.20     77.60     20521.60  1681.60     10260.80     840.80         59.40         4.15         11.18     2.65     99.20

Citrix Xen VM:
Open properties of VM,, select "Startup Options", change "OS Boot Parameters" to "rw init=/bin/bash", graphical utf8reboot, you get  # prompt... if want to edit some files...graphical utf8

graphical utf8

run this command:
# mount -w -o remount / 
# now edit files you want... and reboot... 

#### mysql query to backup table contents into a file.
mysql#> select id,user,subject,content,status,sentdate,last_update from tickets where type='PRODUCT' into outfile '/tmp/product_ticket' fields terminated by '~' lines terminated by '|~|';


Mysql check
mysqlcheck -u root -p --auto-repair -c  -o -A

Repair Mysql MYISAM files..
/myisamchk --force --sort_buffer_size=64M --key_buffer_size=16M --read_buffer_size=8M --write_buffer_size=8M ../data/phplists/phplist_linktrack.MYI

mysql INNODB related
mysql> #SELECT TABLE_SCHEMA, TABLE_NAME, CONCAT(ROUND(data_length / ( 1024 * 1024 ), 2), 'MB') DATA, CONCAT(ROUND(data_free / ( 1024 * 1024 ), 2), 'MB')FREE from information_schema.TABLES where TABLE_SCHEMA='man' and table_name='result10' and Data_free > 0;
mysql> select TABLE_SCHEMA, TABLE_NAME  from information_schema.TABLES where TABLE_SCHEMA='man';

 ALTER TABLE `pass11` ENGINE = InnoDB   (this will also refragment innodb table)

ext4 disable journal

At one high loaded web project I needed a very fast file system. I decided to use Ext4 with disabled journal (As a google:))).

# Create ext4 fs on /dev/sda10 disk
mkfs.ext4 /dev/sda10

# Enable writeback mode. This mode will typically provide the best ext4 performance.
tune2fs -o journal_data_writeback /dev/sda10

# Delete has_journal option
tune2fs -O ^has_journal /dev/sda10

# Required fsck
e2fsck -f /dev/sda10

# Check fs options
dumpe2fs /dev/sda10 |more

For more performance add fstab opions: data=writeback,noatime,nodiratime
/dev/sda10 /opt ext4 defaults,data=writeback,noatime,nodiratime 0 0

Tested at non-boot partition ;)

Redirect port request internally using IPTABLES
# iptables -I PREROUTING -t nat -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080
# rpm -q --provides openssl 
To check which users are connected to ftp servers, make the below entrt in vsftpd.conf

restart vsftpd  and run command
# ps -fe | grep ftp

to restrict users to time based login in system and ftp server

edit /etc/pam.d/vsftpd and add below line just after ending auth section

session    optional     pam_keyinit.so    force revoke
auth       required    pam_listfile.so item=user sense=deny file=/etc/vsftpd/ftpusers onerr=succeed
auth       required    pam_shells.so
auth       include    system-auth
account    required     pam_time.so
account    include    system-auth
session    include    system-auth
session    required     pam_loginuid.so

now edit /etc/security/time.conf and add below line at end.