Here you will get some good tricks and tips on how to monitor a Linux Server or how to manage Linux Server if its causing load, How to find a Spammer, how to check HTTP and MySQL processes.
General Commands
To check the server load and which users are logged on the server with IP address you can fire this command:
w
Monitor performance of various Linux subsystems (CPU, Memory, I/O..) in real time:
sar
sar -u 1 3 : CPU usage of all CPU's.
sar -P 1 3: CPU usage of individual CPU or core.
sar -r 1 3: Memory statistics
sar -b 1 3 : I/O statistics
sar -q 1 3 : Load average statistics
sadc - To get the system activity data:
sa1 - Collect and store binary data in the system activity daily data file
sa2 - Create a report from the current standard system activity daily data file.
sadf - Displaying the contents of data files created by the sar command.
To check for the server load and watch for the processes:
top
top –d2
top –cd2
Monitoring system I/O of the device loading by observing the time the devices are active:
iostat
iostat -x
iostat -c
mpstat - The mpstat command writes to standard output activities for each available processor.
pidstat - The pidstat command is used for monitoring individual tasks currently being managed by the Linux kernel.
nfsiostat - The nfsiostat command displays NFS client per-mount statistics.
cifsiostat - The cifsiostat command displays statistics about read and write operations on CIFS filesystems.
iotop - The iotop command is top like utility for disk I/O. It watches I/O usage information output by the Linux kernel.
iftop - iftop is a command-line system monitor tool that produces a frequently updated list of network connections.
Memory status
free –m
To see all processes running on the server:
ps –aufx
With above commands you can which process is causing load on the server after that, you can go with next steps.
If you see many processes of exim then you can check exim in more detail. shows the total number of email in the queue:
exim –bpc
Print a listing of the messages in the queue:
exim -bp
The following command will show path to the script being utilized to send mail:
ps -C exim -fH eww
ps -C exim -fH eww | grep home
cd /var/spool/exim/input/
egrep "X-PHP-Script" * -R
Shows the number of frozen emails:
exim -bpr | grep frozen | wc -l
To remove FROZEN emails from the server:
exim -bp | exiqgrep -i | xargs exim -Mrm
exiqgrep -z -i | xargs exim –Mrm
Check for spamming if anybody is using php script for sending mail through home
tail -f /var/log/exim_mainlog | grep home
If anyone is spamming from /tmp
tail -f /var/log/exim_mainlog | grep /tmp
To display the IP and number of tries done bu the IP to send mail but rejected by the server:
tail -3000 /var/log/exim_mainlog |grep ‘rejected RCPT’ |awk ‘{print$4}’|awk -F\[ '{print $2} '|awk -F\] ‘{print $1} ‘|sort | uniq -c | sort -k 1 -nr | head -n 5
Shows the connections from a certain ip to the SMTP server
netstat -plan|grep :25|awk {‘print $5′}|cut -d: -f 1|sort|uniq -c|sort -nk 1
To shows the domain name and the number of emails sent by that domain
exim -bp | exiqsumm | more
If spamming from outside domain then you can block that domain or email id on the server
pico /etc/antivirus.exim
Add the following lines:
if $header_from: contains “[email protected]”
then
seen finish
endif
Catching spammer
Check mail stats
exim -bp | exiqsumm | more
Following command will show you the maximum number of email currently in the mail queue have from or to the email address in the mail queue with the exact figure.
exim -bpr | grep “<*@*>” | awk ‘{print $4}’|grep -v “<>” | sort | uniq -c | sort -n
That will show you the maximum number of email currently in the mail queue have for the domain or from the domain with number.
exim -bpr | grep “<*@*>” | awk ‘{print $4}’|grep -v “<>” |awk -F “@” ‘{ print $2}’ | sort | uniq -c | sort -n
Check if any php script is causing the mass mailing with
cd /var/spool/exim/input
egrep “X-PHP-Script” * -R
Just cat the ID that you get and you will be able to check which script is here causing a problem for you.
To Remove particular email account email
exim -bpr |grep “ragnarockradio.org”|awk {‘print $3′}|xargs exim -Mrm
If Mysql causing the load so you can use following commands to check it.
mysqladmin pr
mysqladmin -u root processlist
mysqladmin version
watch mysqladmin proc
If Apache is causing the load so we can check using following commands:
netstat -ntu | awk ‘{print $5}’ | cut -d: -f1 | sort | uniq -c | sort –n
netstat -an |grep :80 |wc –l
netstat -n | grep :80 | wc -l;uptime ; netstat -n | wc –l
netstat –tupl
pidof httpd
history | netstat
lsof -p pid
If MySQL is causing load so you can check it using following commands:
mysqladmin -u root processlist
mysqladmin version
watch mysqladmin proc
mysqladmin -u root processlist
Other Useful Commands
To check pid of php:
pidof php
lsof -p pid
netstat -an |grep :80 |wc –l
netstat -ntu | awk ‘{print $5}’ | cut -d: -f1 | sort | uniq -c | sort -n
netstat -na |grep :80 |sort
Use the below-mentioned command to get top memory consuming processes
ps aux | head -1;ps aux –no-headers| sort -rn +3 | head
Use below command to get top CPU consuming processes
ps aux | head -1;ps aux –no-headers | sort -rn +2 |more
You can check if any backup is going on, run the following commands
ps aux | grep pkg
ps aux | grep gzip
ps aux | grep backup
