Admins eHow

September 1, 2014

Filter out comments and empty lines from config files

Filed under: Bash,linux — Tags: , , , , , — admin @ 12:38 pm
egrep -v "^[[:blank:]]*(#|$)" filename

Send email alerts if Adaptec raid fails in Linux

Filed under: linux — Tags: , , , , — admin @ 10:56 am

For Adaptec Raid you need arcconf tool to check the raid status, you can install it based on the instructions provided on this link (For Debian) :
After you have arcconf installed, create /usr/bin/raidcheck with following content and make it executable :

RESULT=$(arcconf GETCONFIG 1 | grep Status | grep -v "Not Installed" | grep -v Optimal)
if [ -n "$RESULT" ]; then
    wget -O /dev/null
    else echo "Raid is OK"

Note : In my script I have chosen to use a php script on another server to send the alert, this way I wont need to install a mail server on every server which I am monitoring. you can do the same or change the wget line to whatever you want.
Put the script in the cron to check the raid status every 12 hours :

0 */12 * * * /usr/bin/raidcheck

Disable ipv6 on Linux

Filed under: linux — Tags: , , — admin @ 10:17 am

To disable ipv6 on Linux, add following line to /etc/sysctl.conf

net.ipv6.conf.all.disable_ipv6 = 1

Now apply the change :

sysctl -p

August 30, 2014

Backup cPanel accounts to DropBox

Filed under: cPanel,linux — Tags: , , , — admin @ 7:30 pm

Notice : You need root access to cPanel server to be able to use this method.
DropBox is my favorite cloud space provider. Their recent price adjustment (1TB for $10/mo) has made using it a no brainer IMO. It is specially very good for backup purposes because it keeps different versions of your files without using any extra space. The retention period for free accounts is 30 days and for pro accounts is 1 year.
So lets say you take a backup of your website and upload it to DropBox everyday and size of your backup is 100MB. if you keep doing it for 1 year, in fact DropBox is keeping 365 x 100MB of your files which you can retrieve any of them while only 100MB of your space is used! it is crazy good, I know.
In order to be able to backup cPanel accounts directly to DropBox, first we need a method to upload files to DropBox from Linux command line. Fortunately there is a very good solution out there to do it :
Please refer to script documentation on how to install it on your server and link it to your DropBox account. it is fairly easy.
After you linked the script to your DropBox Account, move it to /usr/bin folder.
If you want to test it, run the following command and it should show your DropBox account info :

root@X:[~]: info
Dropbox Uploader v0.14

 > Getting info...

Name:   X X
UID:    012345
Quota:  1021760 Mb
Used:   2611 Mb
Free:   1019148 Mb

Now create /usr/bin/backup2db with following content and make it executable :

for fn in $1; do
/scripts/pkgacct $fn
/usr/bin/ upload /home/cpmove-$fn.tar.gz /cpanel-backup/cpmove-$fn.tar.gz
rm /home/cpmove-$fn.tar.gz

Thats it ! We are good to go.
Command to backup cPanel account acct1 :

backup2db 'acct1'

It even support multiple account backup :

backup2db 'acct1 acct2 acct3'

If you need daily backups, you can put it in cron :

0 0 * * * /usr/bin/backup2db 'acct1 acct2 acct3' > /dev/null 2>&1

August 22, 2014

Kill a process with high CPU usage in Linux

Filed under: linux — Tags: , , , , , — admin @ 5:19 pm

Sometimes you may need to kill hanged processes with high CPU usage automatically. the following script can help you to do it :


L=$(ps aux | grep $PROCESSNAME)
for fn in $L; do
        PID=$(echo $fn | awk '{print $2'})
        LOAD=$(echo $fn | awk '{print $3'})
        if [ $(echo "$LOAD > $HL" | bc -l ) -eq 1 ]
                kill -9 $PID
                echo "Killed $PID"

Set PROCESSNAME to the process name which you want to be checked and HL to high load threshold.
Please note the load is based what ‘ps’ command reports and not what you see inside ‘top’.

August 20, 2014

Force public key authentication on SSH daemon (disable password authentication)

Filed under: Debian,linux,Security — Tags: , , , , , , — admin @ 2:18 pm

It is a very good security practice to completely disable password authentication on your Linux server and use public key authentication method.
In order to do that you need to create your own public/private key pair and put the public key in ~/.ssh/authorized_keys

mkdir -p ~/.ssh
echo 'ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDHV80zPWjPAwKo8Be0k1ypBRMdYDC0H2eQchu3MFsEp8av2F/18GNuHsbyMWp0p1uovP5LGZ/oPZ1ISJxLxxOBiqv0fOyb8uTDYWUUITgGvq9Fppj3BNYTjnLCUAVMKdP3VJ7IPk69ygYR1nhAXiv3dSfeG74f2eo3ZYhrylsVS2G84DUh47FuEFOsfn5s2wXVjwAgqdKBhiVQZWrptf6TEK3fZTVg4rCiRJ+YiIwTZr/CfFHbdqOiwDlGR5fWo0PHHq31lrQXzkASfi3C+ahQFnHsy4+8LdCq+TjzC3J6PbuXP1wpLdm1iP35f61hU1wX2hwhyxdvE+SBXT/PpSVB' >> ~/.ssh/authorized_keys

DISCLAIMER : The above key is my public key, if you put it on your server, I will be able to login into your server :D
Now add/change the following config to /etc/ssh/sshd_config

ChallengeResponseAuthentication no
PasswordAuthentication no
UsePAM no
PubkeyAuthentication yes

and restart ssh service :

service ssh restart

Note : Before closing your current SSH session, I highly recommend you to test that actually you can login into your server by new method. otherwise you may be locked out of your server.

August 9, 2014

Exim Remove All messages From the Mail Queue

Filed under: linux — Tags: , , — admin @ 9:49 pm
exim -bp | exiqgrep -i | xargs exim -Mrm

August 7, 2014

Send email alerts if PERC H200 raid fails in Linux

Filed under: Debian,linux — Tags: , , — admin @ 11:18 pm

Recently I have bought a Dell PowerEdge R210 server which is equipped by PERC H200 raid controller.
As I have setup a raid 1 on this server, I needed to monitor its raid status, Here is what I did :
First you need “sas2ircu” utility which can be found on following website :
Running “sas2ircu 0 STATUS” give you following output :

root@x:/# sas2ircu 0 STATUS
LSI Corporation SAS2 IR Configuration Utility.
Version (2013.03.01)
Copyright (c) 2009-2013 LSI Corporation. All rights reserved.

Background command progress status for controller 0...
IR Volume 1
  Volume ID                               : 79
  Current operation                       : None
  Volume status                           : Enabled
  Volume state                            : Optimal
  Volume wwid                             : xxxxxxxxxxxxxx
  Physical disk I/Os                      : Not quiesced
SAS2IRCU: Command STATUS Completed Successfully.
SAS2IRCU: Utility Completed Successfully.

What we are interested in is “Optimal” status. so if Optimal changes to anything, we want to be notified.
You can use the following script to do that (change MAIL variable to your own email address) :

RESULT=`sas2ircu 0 STATUS | grep Optimal`
if [ -z "$RESULT" ]; then
    echo "RAID ERROR ON SERVER" | mail -s 'Raid Error' "$MAIL"
    else echo "Raid is OK"

as always do not forget to test if your server is actually able to send mails and you receive them.
Finally save the script in a file and put it in cronjob. I have chosen to run it every 12 hours :

0 */12 * * * /usr/bin/raidcheck

July 23, 2014

How to block ongoing DDOS attack on Linux Server

Filed under: General — admin @ 10:44 am

DDOS attacks are one of hardest types of network attacks to encounter and stop. Usually the attacker uses many different IPs to request legitimate resources from your network to the point of exhaustion of your system resources and takes it down.
If you can somehow filter the IP addresses of the attacker on your system, then it is possible to block them in iptables easily and stop the attack.
In my case the attacker was attacking a website hosted on a dedicated IP address, so I was easily able to filter the attacker IP addresses by following command :

netstat -n | grep a.b.c.d | awk '{print $5}' | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' | sort | uniq

a.b.c.d : IP address of my server which the victim website was hosted on
You may do all kinds of filtering using grep and awk.
After I identified attacker IP addresses, blocking them was easy. first create a file named block and put it in /usr/bin with following contents :

iptables -I INPUT -s $1/32 -j DROP

make it executable :

chmod +x /usr/bin/block

then run the following command :

netstat -n | grep a.b.c.d | awk '{print $5}' | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' | sort | uniq | xargs -n1 block

It will automatically block all attacker IPs in server firewall.
You may run the command every 5-10 minutes until the attack stops completely.
The problem of this approach is that you may end up blocking some legitimate users mixed with attacker IPs, but it is still better than having your whole server down indefinitely.
Also after the attack stops, you can remove all firewall rules or simply reboot your server and everything will be good :)

Edit :
In fact you can turn this into a real one liner without creating block file :D, here it is :

netstat -n | grep a.b.c.d | awk '{print $5}' | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' | sort | uniq | xargs -n1 -I {} iptables -I INPUT -s {}/32 -j DROP
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