By default Ubuntu/Debian OS wont load iptable on boot.
So to load iptables on boot use follow procedure:
Save iptable conf with iptables-save command:
iptables-save > /etc/iptables.conf
Next, open file with name /etc/network/if-up.d/iptables and add following content:
iptables-restore < /etc/iptables.conf
Change permission file /etc/network/if-up.d/iptables as executable with following command:
chmod +x /etc/network/if-up.d/iptables
Now, iptables will restored on boot.
Whenever you change iptable rules don’t forgot to update iptables.conf file. Use following command to update iptables.conf file:
iptables-save > /etc/iptables.conf
To set crontab to run on every 5th, 15th, 25th, 35th, 45th, and 55th use following command:
5-55/10 * * * * command
This will execute your command on every 10th minute between 5 mins to 55 mins.
To check if a variable is None use following code:
>>> val is None
If you want to use above example with if condition use following code:
if not (val in None):
print "val is not none"
print "val is none"
While trying to connect memcached using python I got following error:
ImportError: No module named memcache
Since I imported memcache & it’s not available in my server I got the error message saying that “No module named memcache”.
To resolve this issue we need to install python-memcache module.
Use following command to install python-memcache:
$ pip install python-memcache
If your OS is Ubuntu/Debian following command also works for you:
$ apt-get install python-memcache
After installing python-memcache we can seamlessly connect to memcached.
To change nameservers permanently in Ubuntu Desktop Version we need to update /etc/resolvconf/resolv.conf.d/head file with desired list.
Following is the procedure to change nameservers permanently:
Open /etc/resolvconf/resolv.conf.d/head file with your favourite editor:
sudo vim /etc/resolvconf/resolv.conf.d/head
Add following lines to /etc/resolvconf/resolv.conf.d/head, save & exit from the file
Run following command to change nameservers permanently:
sudo resolvconf -u
After running above commands nameservers in your desktop version will get updated with new list as mentioned in /etc/resolvconf/resolv.conf.d/head file.
To conform this open /etc/resolve.conf and validate.
Recently I faced wearied scenario where I am unable to view access logs of lighttpd.
Even though after adding accesslog.filename = “/var/log/lighttpd/access.log” line in lighttpd.conf file logs are not getting updated in lighttpd.conf file
After debugging for a while I seen following error in /var/log/lighttpd/error.log:
WARNING: unknown config-key: accesslog.filename (ignored)
To fix this issue I adding “mod_accesslog” to servers.modules in lighttpd.conf file & restarted lighttpd. After that issue got resolved.
Following is my server.modules after adding mod_accesslog:
server.modules = (
Recently while I am trying to restart HBase I got error message saying that “ERROR: There is a hole in the region chain between …… You need to create a new .regioninfo and region dir in hdfs to plug the hole”.
Following is the error message:
ERROR: There is a hole in the region chain between TestTable,2,1415170922328.3c1b2a210888171d142059912e2faba1. and TestTable,3,1415171044919.da852e5b0034a2ca83f6966280454b4a. You need to create a new .regioninfo and region dir in hdfs to plug the hole.
ERROR: Found inconsistency in table TestTable
To fix this issue you need to stop HBase and delete recover.edits folders for failing regions.
After that start HBase and run hbck which should succeed.
While trying to install some python module I got following exception:
fatal error: Python.h: No such file or directory
Reason for exception:
If you haven’t properly installed the header files and static libraries for python dev this issue may occur.
To resolve this issue install python-dev module by using following command:
$ sudo apt-get install python-dev
fping is a ping like program which uses the Internet Control Message Protocol (ICMP) echo request to determine if a host is up.
With fping we can ping multiple hosts at a time. Use following command to ping multiple hosts:
$ fping -f IPsFiles.txt
where in IPsFiles.txt I have multiple hots.
Below are some other examples of fping:
To ping a host/IP:
$ fping 192.168.2.2
192.168.2.2 is alive
$ fping 192.168.2.22
192.168.1.22 is unreachable
To ping range of IP’s:
$ fping -g 192.168.2.0/24
To list only unreachable hosts/IP’s
$ fping -q -u -f IPsFiles.txt
where -q is for Quiet mode and -u is to list only unreachable targets.
To list only reachable hots/IP’s
$ fping -q -a -f IPsFiles.txt
where -a is to list only alive hots.
While trying to install some module I got error saying that “OpenSSL is not properly installed on your system ubuntu”.
I tried to reinstall this module after installing openssl, but no luck.
After debugging and exploring for a while I got to know that installing libssl-dev could resolve this issue, so I installed libssl-dev with following command:
$ sudo apt-get install libssl-dev
Now retried installation and it worked like charm.