After long time

 Returning to blogger after long time . I took lot of time , but I think I like doing it . 

load mem and cpu for testing

Increase CPU load on server
• dd if=/dev/zero of=/dev/null  -> to increase the cpu
• dd if=/dev/zero of=/dev/null| dd if /dev/zero of=/dev/null -> Multiple run to increase the cpu further

Increase Memory load on server

• dd if=/dev/zero of=/dev/null bs=1G -> to increase the memory load on server

find : useful syntax not regular

Find files with permission 777 (change value as per the search), for dir use type as d
find . type f -perm 0777 -print

Find and correct the permission:
find . -type f -perm 0777 -print -exec chmod 644 {} \;

Find and remove files
find . -type f -name *.javacore -print -exec rm -f {} \;

Find empty files
find /tmp -type f -empty

Find hidden file
find /home type f -name ".*"

Find last 50 days accessed files:
find / -atime 50

Find changed files in last 1 hour:
find / -cmin -60

Find modified files in 60 min:
find / -mmin 60

Find files modified in last 50 days
find / -mtime 50

Find files accessed in last 1 hour:
find / -amin 60

Find 50MB File:
find / -size 50M

Find size 50 - 100 MB:
find / -size +50 -size -100M


Find and delete 100 MB and bigger files:
find / -size +100M -exec rm -f {} \;

Find the files greater than 1 MB and do proper listing
find /home -size +1M -exec ls -lrt {} \;


Find specific type of files and delete

find / -type f -name "*.mp3" -size +10M -exec rm {} \;

Linux Performance Troubleshooting

TOP Command

Command on Server è top

CPU Load Average:

Zombie Process:

%wa (imp): I/O status. Make sure this is close to zero. Higher the number critical will be the health.

%hi: H/W interrupts for CPU happening on server

%si: S/W interrupts for CPU happening on server

%st: This amount of stolen CPU from server to perform operation on shared virtual server to perform some operation.

SWAP Memory: It starts when Physical memory is full. Then Swapping will start moving unused memory blocks to SWAP Memory.

VMSTAT

Command on server à vmstat (e.g. vmstat 10 or vmstat 10 5)

r: how many processes are waiting for CPU time. Higher the value of r , bad the server is behaving. It means issue with CPU

b: wait queue, higher the number of b , it means the issue with disk .

swapd: SWAP memory stats.

free: Free physical memory

buff: before I/O operation

Cache: Mapped by Kernel

si: Swap IN, once swap is started. Disk to Physical

so: Physical to SWAP

bi: Disk I/O, Blocks received from Disk to RAM

bo: Disk I/O , Blocks written to Disk

in: Number of interrupts per sec

cs: Context switches, CPU move from one process to other. Higher means issue with CPU.

IOSTAT

Command on Server à iostat

This provides information related to CPU, Disk

%iowait is important here

Gives details about disk read and write per sec.

SAR

Command on Server à sar

For current and historical details. Linux Package name - sysstat

Collective CPU usage

Memory, SWAP stats

I/O details on server

N/W stats

SAR (historical) on specific time with 10 min of range

SAR version à sar -V

sar 1 2 à output for every 1 sec for two times

sar -f /var/log/sa/sa10  à CPU stats of 10^th (day or date) of the month .

sar -P ALL à Report of all cpu as well as all individual cores

sar -r à memory stats

sar -b à I/O activity (tps à transitions per sec, breads/sec à bytes read per sec )

sar -p -d à I/O Report of all individual disks

sar -w à CPU content (switch to different process)

sar -q à CPU load avg

sar -n à Network stats

sar -n DEV à Enough details for N/W devices for troubleshooting

sar -f /var/log/sa/sa1 -s 00:11:00 -e 00:45:00 à Output of only with start and end time

LSOF

Command on Server à lsof

lsof +D /data à Number of processes opened for directory /data

lsof /var/log/messages à List the files used by any process

lsof -c ssh à Listing the files associated with process (such as sshd process)

lsof /data/ à processes running in specific mount point

lsof -u à Any specific user

lsof -p à For any specific process

FUSER

Command on server à fuser

This displays all the files used by a particular user

fuser -cu /data à This will show user accessing the file-system.

fuser -ck /data à Kill the users accessing the file-system

TCPDUMP

Command on Server à tcpdump

tcpdump -i eth0 à It will capture all the packets on the N/W interface until interrupted (ctrl +c).

tcpdump -c 10 -i eth0 à It will capture 10 packets

tcpdump -w .pcap -i eth0 à Write in file

tcpdump -r .pcap  à Read from file

tcpdump -n -i eth0 à Output will be more readable format

tcpdump -n -i eth0 tcp à Captures only tcp packets

tcpdump -n -i eth0 port 80 à Captures specific to port

tcpdump -i eth0 -s 0 host à This will capture packet between my server and destination server. So basically it captures packet communication between two servers.

Top Running process by CPU and Memory

High Memory processes:

ps -eo pid,ppid,cmd,%mem,%cpu –sort=-%mem | head

ps -eo pmem,pcpu,pidargs | tail -n +2 | sort -rnk 1 | head

ps -eo pmem,pcpu,vsize,pid,cmd | sort -k 1 -nr | head -10

ps axo ruser,%mem,comm,pid,euser | sor -nr | head -n 10

top -b -o +%MEM | head -n 50

-b output top in batch mode

-o for sorting process

-n number of lines (processes)

High CPU processes:

ps -eo pmem,pcpu,pidargs | tail -n +2 | sort -rnk 2 | head

Shell Scripting - referrence

-nt : Newer than
-ot : Older than
-gt : Greater than
-lt : Less than
-ge : Greater than or equal to
-le : less than or equal to
-eq : equal to
-ne : not equal to

check if the name "abc" is file or not
test -f abc; echo $? - if o/p is 0 then its a file else its a directory

also,
[-f abc]; echo $?

to check socket files eg mysql.sock
test -S /var/lib/mysql/mysql.sock; echo $? - if o/p is 0 then its socket file else not

To check null (zero size) files
test -s log1.log; echo $? - if o/p is 0 then its not a zero byte file.

man test - for all details

MySQL - some basic command

Create new Database

create database DataBaseName;

Create User

CREATE USER 'user1'@'localhost' IDENTIFIED BY 'pass1';

Grant privileges on Datatabase

GRANT SELECT,INSERT,UPDATE,DELETE ON *.* TO 'user1'@'localhost'; - limited privileges
or
GRANT ALL ON *.* TO 'user1'@'localhost'; - All privileges
or
GRANT ALL PRIVILEGES ON * . * TO 'sunil'@'localhost' WITH GRANT OPTION MAX_QUERIES_PER_HOUR 0 MAX_CONNECTIONS_PER_HOUR 0 MAX_UPDATES_PER_HOUR 0 MAX_USER_CONNECTIONS 0 ; - root level privileges

Backup Database
mysqldump -u username -p -h hostname DatabaseName > exportedfilename.sql

Restore Database from dump
mysqldump -u username -p -h hostname DatabaseName < mysqldumpfilename.sql

Find version of mysql

select version();

Change Password for user
update user set password=PASSWORD("NEW-PASSWORD-HERE") where User='user';
mysql> flush privileges;

NTP Server restart

/etc/init.d/ntp start
/etc/init.d/ntp stop
/etc/init.d/ntp restart