Syntax for grep to search for a pattern in a file is very well-known. But there are times when one has to grep for the pattern from a certain location or after a certain offset in the file. For example if we are searching for a pattern in a log file which could appear multiple times. Each time we grep, it will provide us all the matching lines from top to bottom of the file and then we have to find which lines were new since our last run. Using dd, the file can be sliced and then grep can be applied for the pattern on that slice. Lets see an example.Continue reading →
dilbert : Working from home
So my boss would not let me work from home. And then I had the rude awakening when I found the reason behind the whole concept of working in office!
Go to the main site by clicking the image and you can read comments by others. I specifically would like to quote one from kattywumpus.
A third form were all possible distractions must be documented, do you have a Dog, how close is the nearest coffee shop, and etc..
snmp : find network information of a system centrally
Anyone can login to a system and run ifconfig or netstat or other similar commands to find the network information of a system. But what will be even better? Do it remotely without logging in to each and every system. How? Using snmpwalk one can retrieve all this information provided that subject has both snmpd running, snmpd supporting network information and the querying host is allowed to make SNMP queries. Lets see how.
Interface table is covered by basic SNMP (just like system information, udp, tcp socket information, address translation and snmp stats etc). Here is how to query the interface table to get the IP address and Subnet mask information.
unixite@sanbox:~/ > snmpwalk -v1 -c public sandboxS:161 1.3.6.1.2.1.4.20.1.1 iso.3.6.1.2.1.4.20.1.1.1.2.3.4 = IpAddress: 1.2.3.4 iso.3.6.1.2.1.4.20.1.1.127.0.0.1 = IpAddress: 127.0.0.1 iso.3.6.1.2.1.4.20.1.1.192.168.1.10 = IpAddress: 192.168.1.10 iso.3.6.1.2.1.4.20.1.1.10.0.0.2 = IpAddress: 10.0.0.2 unixite@sanbox:~/ > snmpwalk -v1 -c public sandboxS:161 1.3.6.1.2.1.4.20.1.3 iso.3.6.1.2.1.4.20.1.3.1.2.3.4 = IpAddress: 255.0.0.0 iso.3.6.1.2.1.4.20.1.3.127.0.0.1 = IpAddress: 255.0.0.0 iso.3.6.1.2.1.4.20.1.3.192.168.1.10 = IpAddress: 255.255.255.0 iso.3.6.1.2.1.4.20.1.3.10.0.0.2 = IpAddress: 255.255.0.0
First one here retrieves the IP addresses on the system while second one get the subnet masks. -c public has to be changed to right community string and also the version if your supports a different one. My system name here is sandboxS and snmpd is listening on default port 161. If not then you can change the port to match yours.
php : find if IP address is in Network range
Using pear Net_IPv4 module one can find if a given IP address is in provided Network range or on the subnet.
<?php
// check if IP falls in provided subnet
include("Net/IPv4.php");
$ipAddr = "192.168.1.8";
$netAddr = "192.168.1.0/29"; // 192.168.1.0 - 192.168.1.7
$objIP = new Net_IPv4();
echo $objIP->ipInNetwork($ipAddr, $netAddr) ? "$ipAddr is in $netAddrn" : "$ipAddr is not in $netAddrn";
?>
This requires pear Net_IPv4 module which can be installing in one of the following ways.
pear install Net_IPv4 php pyrus.phar install pear/Net_IPv4
perl : find if IP address is in Network range
Using NetAddr::IP one can find if a given IP address is in provided Network range or on the subnet. This can take many different representations of the subnet address. For example you can throw at it the CIDR (e.g. 192.168.1.0/29) or explicit start and end addresses (e.g. 192.168.1.0-192.168.1.7) or even with network mask (e.g. 192.168.1.0 mask 255.255.255.248). Following example shows all of these possible cases.
#!/usr/local/bin/perl
use NetAddr::IP;
my $ipAddr = "192.168.1.8";
my $netAddr = "192.168.1.0/29"; # 192.168.1.0 - 192.168.1.7
my $network = NetAddr::IP->new($netAddr);
#my $network = NetAddr::IP->new("192.168.1.0", "255.255.255.248");
#my $network = NetAddr::IP->new("192.168.1.0", "29");
#my $network = NetAddr::IP->new("192.168.1.0-192.168.1.7");
my $ip = NetAddr::IP->new($ipAddr);
if ($ip->within($network)) {
print $ip->addr() . " is in same subnetn";
}
else {
print $ip->addr() . " is outside the subnetn";
}
There are multiple ways the input for network can be provided (four ways are shown above with 3 commented).
bash : search multiple file patterns using single find command
One reader asked how find can be used to find various file patterns. For example in a directory which could be littered with various logs and other files, how do I use a single find command to find all shell scripts, perl scripts and say php scripts. Simple answer is to use multiple -name arguments combined with -o (or ORed) and if needed with -a (or ANDed). Other find conditions (like -mtime, -type etc) can be combined as well.Continue reading →
VirtualBox : Use Raw Disk to load Windows under Linux
Here I explain how to use a Physical disk partition for a guest OS under VirtualBox. This is also called Raw Disk partition use for VirtualBox. My use case was to run WindowsXP as guest OS from a physical installation under Linux and still be able to boot up the system in same Windows installation when needed. My system is running Ubuntu 11.04 on core2 duo, 3GB memory, two hard disks (one with Ubuntu and other with WindowsXP installation), with VirtualBox 4.0.4. Process is simple but took quite a while to get all information/steps collected and tested. In nutshell, first we need to know the partition that we will use, then the user who is going to use it needs to have access to it. After that an mbr has to be created and finally a vmdk file is created to use the Raw Disk. Keep reading for the full process. Continue reading →
perl : Remove empty lines from an array
Using grep the empty lines can be removed from an array in perl. Here is how.
### Remove any empty lines @dataArray = grep(/S/, @dataArray);
Howto rollover a file when size exceeds using unix find
Here is a one liner to rollover a file to file.old when it exceeds the size using find command. Lets say we have a script in cron that runs and prints messages in a log file. Overtime the log file will grow and we would want to rollover the log file to log.old. Many solutions exist by finding the size and comparing it. Here is one elegant solution in one liner. Thanks to my colleague Vlad who gave the idea for using find and exec, and I added the automatic substitution or brace expansion from my knowledge-base. Happy sharing of knowledge.
find /var/log/ -name myapp.log -size +1M -exec mv {}{,.old} ;
Unix : find affected by current working directory
On may Unix variants, find first looks for current working directory before proceeding with what it was asked to find. Ubuntu 10.10 and Debian Squezze not affected and I did not check older versions, but debian 5.0.6 or Lenny is affected and list includes Solaris 10 and Solaris 11 Express. It is very easy to fall in this pitfall if you have some automated package installation which may invoke some scripts for starting applications at the end of installation while cleaning up the temporary directory the package was running from. I wasted couple of hours in going over all my scripts to understand what was going on. The ls command was working but find was not able to get me the list of files to process from unrelated directories. So I ended up redirecting find’s error out to standard out and viola, solution presents itself. That redirection should have been on top of my list. It tells you that “find : cannot get the current working directory”. Why it needs that? I don’t know. Linux has this fixed for some time now, but for some reason SunOS is still using the old find variant including Solaris 11 Express which is the latest version out. Maybe some historical reasons. If anyone know, please share.
So the solution to the problem was that before invoking the command that will continue to run and may need to call find, start it in a directory that will persist after package installation is complete, e.g. / or /tmp.
Continue reading →