Suresh's Tech Notes 1.0 Help

Linux

Command Line Tools

  • Process threads, cpu and memory usage.

    # Show process threads and it's CPU usage $ ps -p <pid> \ -T \ -o start_time,uname,fname,pid,ppid,%cpu,%mem,tid,tname,thcount,time,size,rss,m_size,vsize,lwp | awk '{print $6}' | sort -rn | less # OR $ ps -p <pid> \ -T \ -o start_time,uname,fname,pid,ppid,%cpu,%mem,tid,tname,thcount,time,size,rss,m_size,vsize,lwp --sort -tid # Show all processes sorted by RSS $ ps -eo user,pid,pmem,rss,vsz,comm,start,time,command --sort -rss | numfmt --header --from-unit=1024 --to=iec --field 4-5 | awk '$3 != 0' # Show process tree $ pstree -aps # Show all threads $ ls /proc/<pid>/task # Show all threads using top $ top -H -p <pid>

  • Sysctl

    # /etc/sysctl.conf fs.file-max=10485760 fs.nr_open=10485760 net.core.somaxconn=16192 net.core.netdev_max_backlog=16192 net.ipv4.tcp_max_syn_backlog=16192 net.ipv4.ip_local_port_range = 1024 65535 net.core.rmem_max = 16777216 net.core.wmem_max = 16777216 net.core.rmem_default = 16777216 net.core.wmem_default = 16777216 net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 87380 16777216 net.ipv4.tcp_mem = 1638400 1638400 1638400 net.netfilter.nf_conntrack_buckets = 1966050 net.netfilter.nf_conntrack_max = 7864200 # EC2 Amazon Linux net.core.netdev_max_backlog = 65536 net.core.optmem_max = 25165824 net.ipv4.tcp_max_tw_buckets = 1440000 # /etc/security/limits.conf (set max open file descriptors) * soft nofile 8000000 * hard nofile 9000000

    See 2M websocket connections

    See How TCP backlog works in Linux

    # Can also set it using sysctl commands sysctl -w fs.file-max=12000500 sysctl -w fs.nr_open=20000500 sysctl -w net.ipv4.tcp_mem='10000000 10000000 10000000' sysctl -w net.ipv4.tcp_rmem='1024 4096 16384' sysctl -w net.ipv4.tcp_wmem='1024 4096 16384' sysctl -w net.core.rmem_max=16384 sysctl -w net.core.wmem_max=16384 sysctl -w net.core.somaxconn=1024 ulimit -n 20000000

  • Netstat

    # Find all TCP/UDP listening port's PID $ netstat -tunalp # On Mac $ netstat -vanp tcp | grep -i 8080 # Find process used by given port $ lsof -i :8080 # Socket stats $ ss -s

  • XArgs

    sudo -S pgrep -f tomcat | xargs -n 1 -I {} sh -c 'echo "Killing process pid: {}" && sudo kill -9 {} && echo Done.'

Proc FileSystem

  • Checking the Init system

    case "$(cat /proc/1/comm)" in init) echo Init ;; systemd) echo SystemD ;; upstart) echo Upstart ;; *) echo "unknown: '`cat /proc/1/comm`'" ;; esac # OR $ ps --no-headers -o comm 1 | grep -q 'systemd'

Git Config

These are the common useful git aliases

$ git config --global alias.remote-tags '!git ls-remote --tags --sort="-creatordate" origin | grep -v "\^{}"' $ git config --global alias.remote-tags-short '!git ls-remote --tags --sort="-creatordate" origin | grep -v "\^{}" | cut -f2 | sed "s/refs\/tags\///"' $ git config --global alias.pull-rebase-push '!git pull origin main --rebase && git push origin main --follow-tags' $ git config --global alias.tag-version '!git describe --always --tags --match "v*"'

Curl

  • Get round trip time

    $ curl -X GET \ -o /dev/null \ -I -w "Connect: %{time_connect}s, Transfer: %{time_starttransfer}s, Total: %{time_total}s" \ -X GET http://www.google.com # Curl Response time using specific DNS server $ while true ;do curl \ --dns-servers 8.8.8.8 \ https://suresh.dev \ -o /dev/null \ -s \ -w 'Total: %{time_total}s\n' \ ;done

  • Download the latest release from Github

    # Download the latest release from Github $ LOCATION=$(curl -s https://api.github.com/repos/jvm-profiling-tools/async-profiler/releases/latest \ | grep -i "browser_download_url" \ | grep -i "converter.jar" \ | awk '{ print $2 }' \ | sed 's/,$//' \ | sed 's/"//g' ) \ ; curl --progress-bar -L -o ${HOME}/install/tools/converter.jar ${LOCATION}

  • Download a file with retry

    # -fsSLO $ curl --fail \ --silent \ --show-error \ --location \ --remote-name \ --compressed \ --progress-bar \ --retry 3 \ --retry-connrefused \ --retry-delay 1 \ --connect-timeout 5 \ --max-time 10 \ --request GET \ https://search.maven.org/remotecontent?filepath=org/jetbrains/kotlin/kotlin-stdlib/1.7.0/kotlin-stdlib-1.7.0.jar

DIG

  • Commands

    # Find all nameserver IPs for a TLD $ for i in $(dig ns suresh.dev +short); do echo -n "$i " && dig $i +short; done # Trace DNS requests $ dig +trace compute.suresh.dev # Trace using specific resolver $ dig @a.root-servers.net +trace compute.suresh.dev

SSH

  • Port Forwarding

    # Local Port(2345) Forwarding ssh -v user@ip -L 2345:ip:5432 # ssh -v ooadmin@100.64.0.32 -L 2345:100.64.0.32:5432 # Remote Port Forwarding ssh -v -R :8091:localip:remoteport user@remoteip # ssh -v -R :8091:172.28.170.95:3000 app@10.242.182.199

Wireshark

  • Download wirkshark

  • Install tcpdump on remote host (say 10.9.210.101)

    $ ssh user@10.9.210.101 "sudo yum install -y tcpdump"

  • Start packet capture

    $ ssh user@10.9.210.101 "sudo /usr/sbin/tcpdump -s0 -w - 'port 22'" | wireshark -k -i - # or for 8080 $ ssh user@remote-host "sudo /usr/sbin/tcpdump -s0 -w - 'port 8080'" | wireshark -k -i -

TCPDump

# HTTP traffic including req & res headers and message body from a particular source. $ tcpdump -A -s 0 'src example.com and tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' # All incoming HTTP GET traffic $ tcpdump -i any -s 0 -A 'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420' # All incoming HTTP POST traffic to port 80 $ tcpdump -i any -s 0 -A 'tcp dst port 80 and tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504F5354' # HTTP GET/POST Incoming calls to port 80/443 Originating from 192.168.10.1 Host. $ tcpdump -i any -s 0 -A 'tcp dst port 80 or tcp dst port 443 and tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420 or tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504F5354' and host 192.168.10.1 # Filter HTTP User agents $ tcpdump -vvAls0 | grep 'User-Agent:' # Write to pcap file $ tcpdump -i any -s 0 -X -w /tmp/tcpdump.pcap # Capture TCP packets from local interface $ tcpdump -i lo # Print packet in ASCII $ tcpdump -v -i lo -A

  • https://danielmiessler.com/study/tcpdump/

Last modified: 21 September 2024
JVM ProfilingKotlin