AdminBytes.com

Listing the zombie processes in linux

2011-07-08T00:20:00.001-07:00

# ps aux |perl -ne '{print if ((split(/\s+/))[7] =~ /Z/)}'
abcuser 6005 0.0 0.0 0 0 pts/6 ZN Jun07 0:00 [gcc]
abcuser 7565 0.0 0.0 0 0 pts/6 ZN Jun07 0:00 [csh]
abcuser 7728 0.0 0.0 0 0 pts/222 ZN Jun01 0:00 [gcc]
root 9902 0.0 0.0 0 0 ? Z Apr09 0:00 [sudo]
user1 13420 0.0 0.0 0 0 pts/202 Z+ Jul06 0:00 [grep]
15800 16275 0.0 0.0 0 0 pts/133 ZN+ 12:45 0:00 [csh]
15800 16315 0.0 0.0 0 0 pts/43 ZN+ 12:46 0:00 [csh]
abcuser 19479 0.0 0.0 0 0 pts/6 ZN Jun07 0:00 [gcc]
abcuser 20173 0.0 0.0 0 0 pts/177 Z May24 0:00 [mgdiff]
user6 20808 0.0 0.0 0 0 ? Z May22 0:00 [sh]
abcuser 21001 0.0 0.0 0 0 pts/6 ZN Jun07 0:00 [gcc]
abcuser 21639 0.0 0.0 0 0 pts/222 ZN Jun01 0:00 [csh]

Adding shortcut in vim to compile perl script

2011-06-03T12:19:00.000-07:00

Enter the below line in .vimrc file
map <f5> :w<cr>:!perl %<cr>

netstat quick reference

2010-12-07T05:06:00.000-08:00

Display all LISTENING tcp ports

# Netstat -ntlp

To swtich the name resolution off use

# netstat -tlp

Display all LISTENING udp ports

# netstat -ulp

To see established tcp connections

# netstat -tp

To find out who has connected through ssh

# netstat -ntp|grep :22

# netstat -tp|grep :ssh

Displaying the routing table

# netstat -r

# netstat -rn

Adding IPv6 in linux (RHEL)

2010-12-07T04:52:00.000-08:00

Open /etc/sysconfig/network file, enter:
# vi /etc/sysconfig/network

Append following line:
NETWORKING_IPV6=yes

Open /etc/sysconfig/network-scripts/ifcfg-eth0 (1st network config file)
# vi /etc/sysconfig/network-scripts/ifcfg-eth0
Append following config directives for IPv6:
IPV6INIT=yes
IPV6ADDR=

<IPv6-IP-Address>
IPV6_DEFAULTGW=

<IPv6-IP-Gateway-Address>

Here is a sample file with mix of IPv4 and IPv6 assigned to eth0:
DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
HWADDR=00:30:48:33:bc:33
IPADDR=202.54.1.5
GATEWAY=202.54.1.3
NETMASK=255.255.255.248
IPV6INIT=yes
IPV6ADDR=2607:f0d0:1002:0011:0000:0000:0000:0002
IPV6_DEFAULTGW=2607:f0d0:1002:0011:0000:0000:0000:0001

Where,
• NETWORKING_IPV6=yes|no - Enable or disable global IPv6 initialization.
• IPV6INIT=yes - Enable or disable IPv6 configuration for all interfaces.
• IPV6ADDR=2607:f0d0:1002:0011:0000:0000:0000:0002 - Specify a primary static IPv6 address here.
• IPV6_DEFAULTGW=2607:f0d0:1002:0011:0000:0000:0000:0001 - Add a default route through specified gateway.

Save and close the file. Restart networking:
# service network restart

useful rpm commands and examples

2010-12-06T10:03:00.000-08:00

#rpm -qa
Dumps all installed packages

#rpm -qi httpd
Dumps information about httpd package

#rpm -qf /usr/bin/httpd
Dumps package membership info for file httpd

#rpm -qpi <url>
Shows package info prior to installation

#rpm -Va
Verifies all packages on the system ,returning info only if there are any discrepencies from the original installation

Verfy httpd package for any discrepencies
#rpm -Vf /usr/bin/httpd
SM5 .... T /usr/bin/httpd
Abbreviations (SM5)
S (file size), M (mode or permissions), 5 (MD5), T (mod time)

#rpm -Vp <url>
Verify the remote package in the internet

Installation

rpm -ivh <rpm filename>

Does not override previous package
use this method to install a new version of the kernel

Upgrade (installs or overrides existing package)

#rpm -Uvh <package name>

Freshen (updates an existing package)

Note: Will not install the package ,if it doesn't exist locally

#rpm -Fvh *.rpm - Freshens the current version of a package

Package Removal

#rpm -evh *.rpm - removes a package

Note : Removal process considers dependendies and will complain if the removal will break one or more packages.To get around this,use

#rpm -ev --nodeps *.rpm

Making a file read-only in linux

2010-12-05T00:22:00.000-08:00

#chattr +i file1
This makes the file read only even for the root user

To remove this read only protection
#chattr -i file1

To see the set of extended attributes to a file
#lsattr file1

Iptables quick reference and examples

2010-11-13T02:15:00.000-08:00

Enabling the host to accept all incoming connections to port 80
#iptables -A INPUT -p tcp -s 0/0 --dport 80 -j ACCEPT

Deleting rule 11 from input chain
#iptables -D INPUT 11

Removing all the rules in iptables
#iptables --flush

Saving iptables configuration to a file
#iptables-save > /var/iptables-`date +"%F"`

Restoring iptable configurations from a backup file
#iptables-restore /var/iptables-2010-11-06

Inserting rule no 11 in RH-Firewall-1-INPUT chain
#iptables -I RH-Firewall-1-INPUT 11 -p tcp -s 0/0 --dport 80 -j ACCEPT

Disabling pinging from a particular host
#iptables -I INPUT 1 -p icmp --icmp-type echo-request -s 192.168.1.235 -d 0/0 -j REJECT

Dropping all ping requests
#iptables -I INPUT 1 -p icmp --icmp-type echo-request -s 192.168.1.235 -d 0/0 -j DROP

finding out icmp types available
#iptables -p icmp -h

blocking traffic to a particular port
#iptables -A OUTPUT -p tcp -s 0/0 -d 0/0 --dport 3389 -j DROP

Listing the FORWARD table
#iptables -L FORWARD

Creating a new Chain
#iptables -N APACHE-WEB

Adding the newly created chain to INPUT chain
#iptables -A INPUT -p tcp --dport http:https -j APACHE-WEB

Useful Perl command line examples

2010-11-13T02:12:00.000-08:00

Replacing the contents of all the files in a directory
#perl -pi -e 's/design/dezine/g' *

Retrieving columns using perl
#cat /etc/passwd | perl -e 'while(<>){split /:/;print $_[0],"\n"}'

Note: $_[0] refers to the first column

Retrieving columns with specific matches
#cat /etc/passwd | perl -e 'while(<>){split /:/;print if ($_[0] =~ /mail/)}'

Adding all the values of a particular column
#cat /etc/passwd |perl -e 'while(<>){split /:/;$sum += $_[2]} print $sum'
Above, Adding all data in third column

Mysql DB Backups

2010-09-28T01:54:00.000-07:00

Backing up all the databases

mysqldump --user mysql --password=mysqlpassword --all-databases > /destinationdir/sql.dump_`date +%d-%T`

Backing individual databases and tables

mysqldump --user mysql --password=mysqlpassword --databases DB1 DB2 --tables tbl_testdb > /destinationdir/sql.dump_`date +%d-%T`

Restoring from mysql database
mysql -u root -pmysqlpassword < dumpfile.sql

Finding out the path of installed perl module

2010-08-12T23:08:00.001-07:00

#perldoc perllocal

This comamnd will list the all the installed perl modules in the following format

   Wed Jun 30 00:37:22 2010: "Module" GD::Text
   \uffff\uffff "installed into: /usr/lib/perl5/site_perl/5.8.5"
   \uffff\uffff "LINKTYPE: dynamic"
   \uffff\uffff "VERSION: 0.86"
   \uffff\uffff "EXE_FILES: "

refused connect from xx ip to procedure ypproc_match - (x-domain,byname;-1) error

2010-07-18T23:24:00.000-07:00

The messages log file was getting filled with following error messages

Jul 19 09:57:06 nsserver1 ypserv[6761]: refused connect from 10.25.10.214:33666 to procedure ypproc_match (adminbytes.COM,shadow.byname;-1)

Jul 19 09:54:10 nsserver1 ypserv[6761]: refused connect from 10.25.10.224:42658 to procedure ypproc_match (adminbyts.COM,shadow.byname;-1)

I was able to fix this by updating the /etc/ypserv.conf

Changed the security column from port to none

* : * : shadow.byname : none

* : * : passwd.adjunct.byname : none

Earlier it was

* : * : shadow.byname : port

* : * : passwd.adjunct.byname : port

Listing all apache modules using PHP

2010-07-15T01:31:00.000-07:00

Here is way to list all apache modules using using PHP

<?PHP
print_r(apache_get_modules());
?>

I tried httpd -l ,but it shows only those modules which have been compiled with httpd binary.

#apachectl -t -D DUMP_MODULES -> was not much useful for me

Creating your own certificates for apache using Windows CA

2010-07-07T05:25:00.000-07:00

This article details how to use your own certificate with apache rather than using self generated ones or the the one issued by CA like verisign,geotrust etc..

If you use improper Certificates or self signed certificates ,you get the following message in your browser (IE)

If you dont know how to enable https please go through the below link.
http://wiki.centos.org/HowTos/Https

This article describes how you can issue certificate using Windows certificate Authority server for your apache webserver running on linux.

At Linux/Unix webserver

1) Generate a new private key

# openssl genrsa 1024 > server.key

2) Create a Certificate Request

# openssl req -new -key ./server.key > request.csr

Provide the details.Provide the hostname correctly.These informations will be incorporated into your certificate

3) Copy the contents of request.csr

# cat request.csr

Select all the contents of the file request.csr

Note : Make sure you include ALL the text including —-BEGIN CERTIFICATE REQUEST—- and —-END CERTIFICATE REQUEST—-

At Windows 2003 Certificate Authority

1) Navigate to http://yourCAservername/certsrv and login if prompted

2) Choose Request a Certificate

3) Click "advanced certificate request"

4) Choose Submit a certificate request by using a base-64-encoded CMC or PKCS #10 file, or submit a renewal request by using a base-64-encoded PKCS #7 file

5) In the Saved Request edit box - use control+v to paste the contents of the request.csr file

6) Underneath Certificate Template select Web Server and click the Submit button

Note: If you have sufficient privileges on on the CA, it will be automatically issued to you.Otherwise you need to contact the administrator of the CA server

7) Choose "Download Certifcate link"

8) In the dialog box , save the file as server.crt (by default extension will be .cer file)

9) copy the file server.crt to your linux webserver (using ftp , winscp or any other means )

Back to Linux Webserver (hosting apache)

4) copy the server.crt file to the location /etc/httpd/conf/ssl.crt/

5) copy the server.key file to the location /etc/httpd/conf/ssl.key/

5) Edit the ssl.conf file

# vi /etc/httpd/conf.d/ssl.conf

under the virtual host section (the one using port 443 or which ever secure host you need certificate to be issued), Edit the values for SSLCertificateFile and SSLCertificateKeyFile as mentioned below

SSLCertificateFile /etc/httpd/conf/ssl.crt/server.crt

SSLCertificateKeyFile /etc/httpd/conf/ssl.key/server.key

6) Once this is done , restart the webserver

# /etc/init.d/httd restart

httpd daemon restarts successfully ,if it does not find any discrepencies on the certificates issued

Now open the link in the browser, You wont see the error "website security certificate error".

You will notice the website verified message when you click the "lock" symbol

Related links http://www.yatblog.com/2007/02/27/how-to-create-a-ssl-certificate/

http://www.rtfm-ed.co.uk/2005/01/13/creating-your-own-certificates-for-the-mui/

MySQL Root password recovery

2010-07-05T10:57:00.000-07:00

http://www.linuxquestions.org/linux/answers/Security/MySQL_root_password_recovey

Creating Virtual hosts in Apache

2010-07-04T11:15:00.000-07:00

Virtual hosts helps the webserver to host multiple websites on a single webserver.You can have website1.com and website2.com to point to the same webserver.

Apache supports creating virtual hosts in two ways
1) Name based virtual host
2) IP Based virtual host

Name Based Virtual Hosting
This method allows Virtual hosts to be created using a single IP address.All the websites on a webserver can share a single IP address.THis method is quite handy ,when IP addresses are limited and are a costly affair.

First you need to have DNS entries pointing to this host machine.

Just a alias/CNAME to the host IP address in DNS will do.

DNS Entries should be something like mentioned below.

webhost A 10.10.100.201 ; Physical webhost for virtual hosts

website1 CNAME webhost

website2 CNAME webhost

Then ,add the following entries in httpd.conf file
#----------------------

NameVirtualHost *:80

<VirtualHost *:80>
   ServerName website1
   DocumentRoot "/var/webapps/website1/html"
   ErrorLog logs/website1_error_log
</VirtualHost>

<VirtualHost *:80>
   ServerName website2
   DocumentRoot "/var/webapps/website2/html"
   ErrorLog logs/website2_error_log
</VirtualHost>

#-----------------------

You can use most of the HTTP directives that are used in httpd.conf

Once the httpd.conf file is updated restart httpd daemon
/etc/init.d/httpd restart

Disadvantage of Name based Virtual Hosting
1)They do not properly support secure websites (HTTPS
2) If the Domain Name System is malfunctioning, it is harder to use a name-based virtually-hosted website
3) They will not work with browsers that do not send the hostname as part of requests
4) Improperly configured file permissions with shared file systems might give other (compromised) users or processes system-wide access to these files.

IP Based Virtual Hosting
IP based virtual hosting method requires that all the websites should have an IP address to identify them.
IP based virtual hosting overcomes limitations of Name based Virtual hosting.

To add IP based, you need to have DNS entries for each website to point to the corresponding IP address.
You also need to have multiple IP addresses on the host machine either by using multiple NIC cards or creating virtual IP addresses.

Refer the below link for creating virtual IPs
http://wiki.centos.org/TipsAndTricks/VirtualIPAddresses?highlight=(virtual)|(IP))

Once virtual IP addresses are created , add the following entries in httpd.conf. I am taking 172.16.212.233 and 172.16.212.233 as virtual IPs
--------------------------------

<VirtualHost 172.16.212.233:80>
   ServerName website1
   DocumentRoot "/var/webapps/website1/html"
   ErrorLog logs/websote1_error_log
</VirtualHost>

<VirtualHost 172.16.212.234>
   ServerName website2
   DocumentRoot "/var/webapps/website2/html"
   ErrorLog logs/website2_error_log
</VirtualHost>

--------------------------------

You would have noticed the entry <VirtualHost 172.16.212.233:80>
I have mentioned port 80 as there is SSL website running for the same IP address on port 443.

You need to restart httpd daemon for the changes to take effect.

Obtain specific user, group, and process information using Perl functions

2010-06-30T22:26:00.001-07:00

Function	Explanation	Example
getpwnam($name)	This function returns the password file entry for the user $name. Use this function to retrieve information about a user, given the user's login name on the system.	Code: #!/usr/bin/perl # get user info ($name, $pass, $uid, $gid, $quota, $comment, $gcos, $dir, $shell, $expire) = getpwnam('victor'); print "Name: $name \nUID: $uid \nShell: $shell\n"; Output: Name: victor UID: 1000 Shell: /bin/bash
getpwuid($id)	This function returns the password file entry for the user ID $id. Use this function to retrieve information about a user, given the user ID.	Code: #!/usr/bin/perl # get user info ($name, $pass, $uid, $gid, $quota, $comment, $gcos, $dir, $shell, $expire) = getpwuid(1000); print "Name: $name \nUID: $uid \nShell: $shell\n"; Output: Name: victor UID: 1000 Shell: /bin/bash
getpwent()	This function returns the next available line from the system password file. Use this function in a loop to process the system password file line by line.	Code: #!/usr/bin/perl # get user info while (($name, $pass, $uid, $gid, $quota, $comment, $gcos, $dir, $shell, $expire) = getpwent()) { print "$name \t $uid \t $dir\n"; } Output: root 0 /root bin 1 /bin daemon 2 /sbin adm 3 /var/log lp 4 /var/spool/lpd sync 5 /sbin shutdown 6 /sbin halt 7 /sbin mail 8 /
getgrnam($name)	This function returns the group file entry (including the member list) for the group $name. Use this function to retrieve information about a user, given the group name.	Code: #!/usr/bin/perl # get group info ($name, $passwd, $gid, $members) = getgrnam('wheel'); print "$name \t $gid \t $members\n"; Output: wheel 10 root
getgrgid($id)	This function returns the group file entry (including the member list) for the group ID $id. Use this function to retrieve information about a group, given the group ID.	Code: #!/usr/bin/perl # get group info ($name, $passwd, $gid, $members) = getgrgid(1); print "$name \t $gid \t $members\n"; Output: bin 1 root bin daemon
getgrent()	This function returns the next available line from the system group file. Use this function in a loop to process the system's groups one after another.	Code: #!/usr/bin/perl # get group info while (($name, $passwd, $gid, $members) = getgrent()) { print "$name \t $gid \t $members\n"; } Output: root 0 root bin 1 root bin daemon daemon 2 root bin daemon sys 3 root bin adm adm 4 root adm daemon tty 5 disk 6 root adm
getlogin()	This function returns the name of the currently logged-in user. Use this function to identify which user is currently logged in and/or which user the script is currently running as.	Code: #!/usr/bin/perl # get logged-in user name print "Current user is " . getlogin(); Output: Current user is joe
getpgrp($id)	This function returns the process group for the PID $id. When the PID is 0, it returns the process group for the current process. Use this function to obtain the current process ID.	Code: #!/usr/bin/perl # get current process ID print "Current PID is " . getpgrp(0); Output: Current PID is 403
getppid()	This function returns the ID for the parent of the currently-executing process. Use this function to obtain the current process's parent ID (for interactive scripts, this is usually the PID of the controlling terminal).	Code: #!/usr/bin/perl # get parent process ID print "Current process' parent PID is " . getppid(); Output: Current process' parent PID is 111

Configuring new directory for CGI scripts in apache

2010-06-17T22:57:00.000-07:00

Add the following entries in httpd.conf

ScriptAlias /scripts/ "/var/scripts/"

Options +ExecCGI
AddHandler cgi-script cgi pl
AllowOverride all
Options None
Order allow,deny
Allow from all

Setting up SSL port forwarding in LINUX

2010-06-02T00:24:00.000-07:00

# iptables -t nat -A PREROUTING -p tcp --dport 443 -j REDIRECT --to 8443
# service iptables save
Saving firewall rules to /etc/sysconfig/iptables: [ OK ]

Using SQL in Shell script

2010-04-26T00:40:00.001-07:00

mysql -h host_name -u username --password=password <<EOF

use database_name ;
insert into test(name,place) values('admin','india');
select * from test;
EOF

Inplace edit for multiple files

2010-04-21T05:07:00.001-07:00

Inplace edit for multiple files
perl -pi -e 's/http/https/g' *

Using Sessions Variables in CGI page

2010-04-19T23:13:00.000-07:00

First include the following module

#-----------------------Webpage 1 ----------------
use CGI::Session
#Creating a session and initialising a session
my $session = new CGI::Session();
my $CGISESSID = $session->id();
$session->param( "ses_username", $LDAPUser );
$session->flush();
#-------------------------------------------------

Now lets see how to read this session variales from page 2
First You need to pass the session id through query string or hidden values

#-----------------------Webpage 1 ----------------
Use CGI::Session;
my $sesid = $query->param("ses_id");
my $session = CGI::Session->load($sesid);
my $user = $session->param("ses_username");
#-------------------------------------------------

Perl script for displaying files more than N days old

2010-04-10T04:33:00.000-07:00

my $DIR='/home/files/';
my $mtimesec;
my $MAXDAYS=2;
my $maxdays=60*60*24*$MAXDAYS;
opendir(DIR,$DIR)|| die "$!";
while ( my $filename = readdir(DIR)) {
 if(-f $DIR.'/'.$filename) {
  $mtimesec=(stat($filename))[9];
  if((time-$mtimesec) > $maxdays) {
      print "$filename\n";
  }
 }
}

Managing Hard disk settings in Linux

2010-04-10T02:41:00.000-07:00

Displaying Harddisk parameters
#hdparm -I /dev/sda

Setting Harddisk parameters
#hdparm -W 1 /dev/sda

Retaining the settings across soft reboot
#hdparm -K 1 /dev/sda

Checking Disk utilisation in Linux

2010-03-23T23:14:00.000-07:00

# iostat -d -x 1
Linux 2.6.29.4 (l-sim-02-120) 03/23/2010

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
hda 0.13 17.93 0.19 3.78 14.61 173.74 7.31 86.87 47.44 0.37 92.98 3.45 1.37
hda1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 14.37 0.00 8.93 8.40 0.00
hda2 0.12 0.33 0.04 0.00 1.30 2.68 0.65 1.34 89.87 0.01 158.33 8.17 0.04
hda3 0.00 17.60 0.15 3.77 13.31 171.06 6.65 85.53 46.97 0.36 92.24 3.46 1.36

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
hda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
hda1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
hda2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
hda3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Running a command from history in LINUX

2010-03-23T23:12:00.001-07:00

host1#history
1 22:03 cd /home/tools
2 22:03 cd /home/cpu
3 22:06 env|grep -i path|grep -v something

To run 3rd command again from history ,use

host1# !3