Linux
Posted on :: 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
     # 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/
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