howto

HOW TO : count lines in windows command line

Say you are using netstat to checl all established network connections on a windows machine (confirmed to work on windows 7+ and windows server 2008+) and want to find out how many connections you have, you can use

netstat -an | find "ESTABLISHED" | find /v /c ""

breaking down the command string

netstat -an : Uses netstat command to display all connections and listening ports (-a) and displays them in numerical form instead of resolving DNS or using common names (-n)

| : piping (passing) output of one command to the next one

find “ESTABLISHED” : Uses find command to filter out to just lines that contain the string “ESTABLISHED”‘

find /c /v “” : exclude blank lines (/v “”) and count the number of remaining lines (/c)

If you wanted to something similar in linux, you can use

netstat -an | grep "ESTABLISHED" | wc -l
May 30, 2016 by HOWTO Technology Uncategorized Windows 0

HOW TO : Use grep to search for content at end of line

If you want to search for a pattern at the end of a line, you can use

tail -f logfile | grep -v "0$"

breaking down the commands

tail -f : standard tail command. Continuous output to console as the file grows (or until it ends)

grep -v : -v command forces grep to show content that doesn’t match pattern

0$ : This regex is specifically looking for a 0 at the end of the line, which is denoted by $.

February 2, 2016 by Linux Technology Uncategorized 0

HOW TO : Query varnishlogs for requests with 404 responses

varnishlog, one of the tools provided with varnish cache, uses VSL Query Expressions (https://www.varnish-cache.org/docs/trunk/reference/vsl-query.html) to provide some powerful insights into the requests and responses.

Here is a how you can use varnishlog to show all client requests that are ending up with a 404 response.

sudo varnishlog -g request -i ReqURL -q "BerespStatus != 200"

Technically, this particular query shows all client requests with a response other than 200.

Breaking down the commands

-g request : shows all entries related to the request

-i ReqURL : forces varnishlog to only display the Requesting URL

-q “BerespStatus != 200” : query filter to only match non 200 responses. Note that the query has to be enclosed in “”.

February 1, 2016 by HOWTO Linux Networking Technology Uncategorized Web 0

HOW TO : Enable wildcard domains in Squid

We were trying to modify some ACL (access control lists) in squid to allow traffic to certain websites. Instead of adding each individual hostnames in a domain, we wanted to add all traffic to a certain domain.

Document on the interwebs is old or not clear on how to achieve this.

After some trial and error, here is what works

say you want to allow all traffic to the google.com domain, you create a access list using dstdomain like below

acl name_of_acl dstdomain .google.com

The “.” before the domain name acts as a wildcard

Then you use the acl to allow http access to it like below

http_access allow name_of_acl
December 15, 2015 by HOWTO Networking Technology Uncategorized 0

HOW TO : Capture network traffic on a Solaris server

If you don’t have tcpdump installed on your solaris server, you can use the “snoop” system command to capture network traffic.

Here is the command line option to capture 1000 packets of network traffic from IP 192.168.10.10 on a solaris server using inteface e1000g1 and write the output to /tmp/capture.pcap

snoop -d e1000g1 -c 10000 -o /tmp/capture.pcap host 192.168.10.10

Details of the command options

  • -d : Name of the interface you want to capture traffic on
  • -c : Number of packets you want to capture
  • -o : Path to the output file
  • host : IP address of the host you want to capture traffic from and to

More details at https://docs.oracle.com/cd/E23824_01/html/821-1453/gexkw.html

PS : You have to have root privileges to run this command.

November 23, 2015 by HOWTO Technology Uncategorized 0

HOW TO : Use awk to print values larger than certain number

Quick how to on using awk to filter results if a certain value (column) is larger than a set value.

For example, if you have a file (servers.txt) with lines in this format

a_datacenter, servers 20
 error, servers xyz
 b_datacenter, servers 21
 c_datacenter, servers 50

and you want to show only the lines that have server value larger than 20, you can do this in awk by running

grep datacenter servers.txt | awk '$3 > 20  {print ;}' | more

breaking down the commands

grep – parsing down the output to just show the lines containing datacenter

awk – $3 > 20 : Get the third variable (awk seperates text using spaces by default) and check if it is greater than 20

print – print the entire line

August 24, 2015 by HOWTO Linux Technology Uncategorized 0

HOW TO : Find files, search for content in them, replace the content

The title pretty much says it all :). Here is a quick  one liner, using multiple tools, to look for files in a directory, search for certain content in them and replace them with other content

[code]find -type f | xargs grep -l ORIGINAL_CONTENT | xargs perl -p -i -e ‘s/ORIGINAL_CONTENT/NEW_CONTENT/g’ [/code]

You can theoretically take out the grep (second command) and directly pipe the find output to perl and get the same outcome.

Going over list of the options used

find

  • “-type f” lists all objects of type file in the directory (and sub directories)

grep

  • “-l” lists the names of the files (with relative path) which have the text ORIGINAL_CONTENT in them

perl

  • “-p” forces perl to loop through requests. In this case files
  • “-e” tells perl that the next argument is a perl statement
  • “-i” tells perls to edit the file in place (i.e. no need for an output file)
August 16, 2012 by Linux Technology Uncategorized 0