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Linux System Diagnostic Tools

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Show utilization of each CPU individually.

mpstat -P ALL

Sampling CPU usage in 2 seconds frame for 5 times

sar -u 2 5

Can also be found in logs

sar - f /var/log/sysstat/sa09

See who is eating CPU

ps -eo pcpu,pid,user,args | sort -k 1 -r | head -10

Show I/O stats every 5 seconds

iostat -xtc 5

Show resource stats using megabyte as unit

vmstat -S M 2 5

Show NFS stats


Find memory used by a process using pmap

pmap <pid>

Display sockets summary

ss -s

Show open sockets with process name

ss -pl

show all ports connected from remote port

ss dst
ss dst 
ss dst

Find out all ips connected to ip address x.x.x.x, where x.x.x.x is the machine's ip address

ss src x.x.x.x

Show all connections

netstat -nat

Detect DDoS attack

netstat -atun | awk '{print $5}' | cut -d: -f1 | sed -e '/^$/d' |sort | uniq -c | sort -n

Summary statistics by protocol

netstat -s

View system call stacks of a process

strace -o output.txt /bin/foo
strace -p 12345 -s 80 -o /tmp/debug.httpd.txt
strace -e trace=open,read -p 22254 -s 80 -o debug.http.txt


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