All posts in DevOps

Linux commands that DevOps engineers (or SysAdmin) should know.

ref:
https://peteris.rocks/blog/htop/
http://techblog.netflix.com/2015/11/linux-performance-analysis-in-60s.html
http://techblog.netflix.com/2015/08/netflix-at-velocity-2015-linux.html

總覽

$ top

$ sudo apt-get install htop
$ htop

# 每 1 秒輸出一次資訊
$ vmstat 1
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 1  0      0 1580104 171620 4287208    0    0     0    11    2    2  9  0 90  0  0
 0  0      0 1579832 171620 4287340    0    0     0     0 2871 2414 13  2 85  0  0
 0  0      0 1578688 171620 4287344    0    0     0    40 2311 1700 18  1 82  0  0
 1  0      0 1578640 171620 4287348    0    0     0    48 1302 1020  5  0 95  0  0
...

查 CPU

$ uptime

Load average: 0.03 0.11 0.19
Load average: 一分鐘 五分鐘 十五分鐘內的平均負載
單核心，如果 Load average 是 1 表示負載 100%
多核心的話，因為 Load average 是所有 CPU 數加起來，所以數值可能會大於 1

$ sudo apt-get install sysstat

# 每個 CPU 的使用率
$ mpstat -P ALL 1
Linux 3.13.0-49-generic (titanclusters-xxxxx)  07/14/2015  _x86_64_ (32 CPU)
07:38:49 PM  CPU   %usr  %nice   %sys %iowait   %irq  %soft  %steal  %guest  %gnice  %idle
07:38:50 PM  all  98.47   0.00   0.75    0.00   0.00   0.00    0.00    0.00    0.00   0.78
07:38:50 PM    0  96.04   0.00   2.97    0.00   0.00   0.00    0.00    0.00    0.00   0.99
07:38:50 PM    1  97.00   0.00   1.00    0.00   0.00   0.00    0.00    0.00    0.00   2.00
07:38:50 PM    2  98.00   0.00   1.00    0.00   0.00   0.00    0.00    0.00    0.00   1.00
...

# 每個 process 的 CPU 使用率
$ pidstat 1
Linux 3.13.0-49-generic (titanclusters-xxxxx)  07/14/2015    _x86_64_    (32 CPU)
07:41:02 PM   UID       PID    %usr %system  %guest    %CPU   CPU  Command
07:41:03 PM     0         9    0.00    0.94    0.00    0.94     1  rcuos/0
07:41:03 PM     0      4214    5.66    5.66    0.00   11.32    15  mesos-slave
07:41:03 PM     0      4354    0.94    0.94    0.00    1.89     8  java
07:41:03 PM     0      6521 1596.23    1.89    0.00 1598.11    27  java
...

查 Memory

$ free –m
             total       used       free     shared    buffers     cached
Mem:          7983       6443       1540          0        167       4192
-/+ buffers/cache:       2083       5900
Swap:            0          0          0

查 Disk

$ iostat -xz 1
Linux 3.13.0-49-generic (titanclusters-xxxxx)  07/14/2015  _x86_64_ (32 CPU)
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          73.96    0.00    3.73    0.03    0.06   22.21
Device:   rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
xvda        0.00     0.23    0.21    0.18     4.52     2.08    34.37     0.00    9.98   13.80    5.42   2.44   0.09
xvdb        0.01     0.00    1.02    8.94   127.97   598.53   145.79     0.00    0.43    1.78    0.28   0.25   0.25
xvdc        0.01     0.00    1.02    8.86   127.79   595.94   146.50     0.00    0.45    1.82    0.30   0.27   0.26

查 Disk Usage

# show whole disk
$ df -h

# show every folder under the directory
$ du -h /data

# show the top directory only
$ du -hs /var/lib/influxdb/data
77.4G    /var/lib/influxdb/data

# show largest top 10 files
$ du -hsx * | sort -rh | head -10

ref:
https://www.codecoffee.com/tipsforlinux/articles/22.html
https://www.cyberciti.biz/faq/how-do-i-find-the-largest-filesdirectories-on-a-linuxunixbsd-filesystem/

查 IO

$ sudo apt-get install dstat iotop

# 可以顯示哪些 process 在進行 io 操作
$ dstat --top-io --top-bio

# with –only option to see only processes or threads actually doing I/O
$ sudo iotop --only

ref:
https://www.cyberciti.biz/hardware/linux-iotop-simple-top-like-io-monitor/

查 CPU bound 或 IO bound

$ iostat -c | head -3 ; iostat -c 1 20

ref:
https://serverfault.com/questions/72209/cpu-or-network-i-o-bound
https://askubuntu.com/questions/1540/how-can-i-find-out-if-a-process-is-cpu-memory-or-disk-bound

iotop cannot is not working inside a container.

查 Process

$ ps aux
$ pstree -a

# attach to a process to find out system calls the process calls
# -t -- absolute timestamp
# -T -- print time spent in each syscall
# -s strsize -- limit length of print strings to STRSIZE chars (default 32)
# -f -- follow forks
# -e -- filtering expression: `option=trace,abbrev,verbose,raw,signal,read,write,fault`
# -u username -- run command as username handling setuid and/or setgid
$ strace -t -T -f -s 2048 -p THE_PID

# find out which files that nginx accesses
# you could try to find something related to the error message first:
# write(1, "Ign http://192.168.212.136 trusty Release\n", 62) = 62
# writev(12, [{"HTTP/1.1 500 Internal Server Error"..., 256}, {...}, {...}, {...}, 4]) = 276
$ strace -f -e trace=file service nginx start

# 顯示 PID 3001 的 process 是用什麼指令和參數啟動的
$ tr '\0' '\n' < /proc/3001/cmdline

# only on macOS
$ top -c a -p 1537

ref:
https://mp.weixin.qq.com/s/Sf79W5dqUFx7rUYRrtx88Q
https://blogs.oracle.com/linux/strace-the-sysadmins-microscope-v2
https://zwischenzugs.com/2011/08/29/my-favourite-secret-weapon-strace/

查 Kernel Logs

# 顯示最近的 15 筆 system messages
$ dmesg | tail -fn 15

# 顯示有關 killed process 的 logs
$ dmesg | grep -E -i -B50 'killed process'

ref:
https://stackoverflow.com/questions/726690/what-killed-my-process-and-why

查 Network

$ sar -n TCP,ETCP 1

查 DNS

Resolve a domain name using dig:

$ apt-get install curl dnsutils iputils-ping
# or
$ apk add --update bind-tools

$ dig +short october-api.default.svc.cluster.local
10.32.1.79

$ dig +short redis-broker.default.svc.cluster.local
10.60.32.20
10.60.33.15

$ dig +short redis-broker-0.redis-broker.default.svc.cluster.local
10.60.32.20

ref:
https://blog.longwin.com.tw/2013/03/dig-dns-query-debug-2013/

Resolve a domain name using nslookup:

$ apt-get install dnsutils

$ nslookup redis-broker.default.svc.cluster.local
Server:    10.3.240.10
Address 1: 10.3.240.10 kube-dns.kube-system.svc.cluster.local

Name:      redis-broker.default.svc.cluster.local
Address 1: 10.0.69.46 redis-broker-0.redis-broker.default.svc.cluster.local

Find specific types of DNS records:

$ nslookup -q=TXT codetengu.com
Server:     1.1.1.1
Address:    1.1.1.1#53

Non-authoritative answer:
codetengu.com    text = "zoho-verification=xxx.zmverify.zoho.com"

Authoritative answers can be found from:

nslookup could return multiple A records for a domain which is commonly known as round-robin DNS.

ref:
https://serverfault.com/questions/590277/why-does-nslookup-return-two-or-more-ip-address-for-yahoo-com-or-microsoft-com

查 Nginx

# 顯示各個 status code 的數量
$ cat access.log | cut -d '"' -f3 | cut -d ' ' -f2 | sort | uniq -c | sort -rn

# 顯示哪些 URL 的 404 數量最多
$ awk '($9 ~ /404/)' access.log | awk '{print $7}' | sort | uniq -c | sort -rn

# 顯示 2016/10/01 的 16:00 ~ 18:00 的 log
$ grep "01/Oct/2016:1[6-8]" access.log

# 顯示 2016/10/01 的 09:00 ~ 12:00 的 log
$ egrep "01/Oct/2016:(0[8-9]|1[0-2])" access.log

ref:
http://stackoverflow.com/questions/7575267/extract-data-from-log-file-in-specified-range-of-time
http://superuser.com/questions/848971/unix-command-to-grep-a-time-range

如果 status code 是 502 Bad Gateway
通常表示是 load balancer / nginx 的 upstream server 掛了或連不到
如果是 Kubernetes service 的話
可能是 Service spec.selector 跟 pod 匹配不起來

50 Most Frequently Used UNIX / Linux Commands
http://www.thegeekstuff.com/2010/11/50-linux-commands/

Write a Simple Script in Shell

Write a for loop.

$ for pod_name in $(kubectl get pods -l app=swag-worker-test -o jsonpath={..metadata.name}); do; kubectl delete pod $pod_name; done
pod "swag-worker-test-67fffcdd5-5hgf3" deleted
pod "swag-worker-test-67fffcdd5-h8jgg" deleted

# you could also write multiple lines
for pod_name in $(kubectl get pods -l app=swag-worker-test -o jsonpath={..metadata.name}); do
    kubectl delete pod $pod_name
done

Write a while true.

# using trap and wait will make your container react immediately to a stop request
$ bash -c "trap : TERM INT; sleep infinity & wait"
# or
$ bash -c "while true; do echo 'I am alive!'; sleep 3600; done"

or

#!/bin/bash
while true; do echo 'I am alive!'; sleep 3600; done

ref:
https://stackoverflow.com/questions/31870222/how-can-i-keep-container-running-on-kubernetes

Set Environment Variables from a File

$ export $(cat .env | grep -v ^# | xargs)

ref:
https://stackoverflow.com/questions/19331497/set-environment-variables-from-file

Switch to Another User

# the latter with "-" gets an environment as if another user just logged in
$ sudo su - ubuntu

Clear the Content of a File

$ echo -n > /var/log/nginx/error.log

ref:
https://unix.stackexchange.com/questions/88808/empty-the-contents-of-a-file

Pipeline stdout with xargs

$ find . -type f -name "*.yaml" | xargs echo
./configmap.yaml ./pvc.yaml ./service.yaml ./statefulset.yaml

$ find . -type f -name "*.yaml" | xargs -n 1 echo
./configmap.yaml
./pvc.yaml
./service.yaml
./statefulset.yaml

$ find . -type f -name "*.yaml" | xargs -n 2 echo
./configmap.yaml ./pvc.yaml
./service.yaml ./statefulset.yaml

$ redis-cli KEYS "*-*-*-*.reply.celery.pidbox" | xargs -n 100 redis-cli DEL

ref:
https://shapeshed.com/unix-xargs/

Set a Timeout for any Command

$ timeout -t 15 celery inspect ping -A app:celery -d celery@$(hostname)

Run a One-time Command at a Specific Time

at executes commands at a specified time. You may need to install the "at" package manually.

# install
$ sudo apt-get install at

# start
$ sudo atd

# list jobs
$ atq

$ at 00:05
at> echo "123" > /tmp/test.txt

$ at 00:00 18.1.2017
at> DPS_ENV=production /home/ubuntu/.virtualenvs/dps/bin/python /home/ubuntu/dps/manage.py send_emails > /tmp/send_emails.log

Press Control + D to exit at shell.

ref:
https://www.lifewire.com/linux-command-at-4091646
https://tecadmin.net/one-time-task-scheduling-using-at-commad-in-linux/

Pass Arguments to bash when Executing a script Fetched by curl

$ curl -L http://bit.ly/open-the-pod-bay-doors | bash -s -- --tags docker 

ref:
https://stackoverflow.com/a/25563308/885524
https://github.com/vinta/HAL-9000

Change a File's Modify Time

$ touch -m -d '1 Jan 2006 12:34' tmp
$ touch -m -d '1 Jan 2006 12:34' tmp/old_file.txt

ref:
https://www.unixtutorial.org/2008/11/how-to-update-atime-and-mtime-for-a-file-in-unix/

Delete Old Files under a Directory

$ find /data/storage/tmp/* -mtime +2 | xargs rm -Rf
$ find /data/storage/tmp/* -mtime +2 -exec rm {} \;

ref:
http://stackoverflow.com/questions/14731133/how-to-delete-all-files-older-than-3-days-when-argument-list-too-long

Append String to a File

# append
$ echo "the last line" >> README.md

# replace
$ echo "replace all" > README.md

Rename Sub-folders

$ for f in */migrations/; do mv -v "$f" "${f%???????????}south_migrations"; done

ref:
http://unix.stackexchange.com/questions/220176/rename-specific-level-of-sub-folders

List History Commands

$ export HISTTIMEFORMAT="%Y%m%d %T  "
$ history

Make Permission For A File Same As Another File

$ chmod --reference=file1 file2

Find Computer's Public IP

$ wget -qO- http://ipecho.net/plain ; echo

ref:
http://askubuntu.com/questions/95910/command-for-determining-my-public-ip

Compress and Uncompress Files

$ tar czf media-20151010.tar.gz media/
$ s3cmd put media-20151010.tar.gz s3://goeasytaxi/

# decompress
$ tar -xzf media.tar.gz

$ sudo apt-get install zip unzip
$ zip -j -r deps.zip spark_app/src/deps/
$ zip -r hourmasters.zip hourmasters/
$ scp -r -i ~/hourmasters.pem ssh [email protected]:/home/ubuntu/hourmasters.zip ~/Desktop/

# decompress
$ unzip stork.1.4.zip
$ gzip -d uwsgi.log.*.gz

$ gzip dps.201701171200.sql
$ gunzip dps.201701171200.sql.gz

Count File Lines

$ wc -l filename.txt

$ wc -l *.py

Find Files by Name or Content

$ find / -name virtualenvwrapper.sh

# 在現在的資料夾裡的全部檔案中搜尋字串，會自動搜尋子目錄
$ find . | xargs grep 'string'

$ find . -iname '*something*'

$ find *.html | xargs grep 'share_server.html'

# 搜尋當前目錄及子目錄下的含有 print() 字串的檔案
$ grep -rnw "." -e "print()"

$ grep -rnw "." -e "print()" --include=\*.py

ref:
https://stackoverflow.com/questions/16956810/how-do-i-find-all-files-containing-specific-text-on-linux

Find Directories by Name

$ find . -type d -name "*native*" -print

ref:
https://askubuntu.com/questions/153144/how-can-i-recursively-search-for-directory-names-with-a-particular-string-where

List Files by Date

$ ls -lrt

List Files Opened by a Process

$ lsof | grep uwsgi

$ lsof -i | grep LISTEN
$ lsof -i -n -P | grep LISTEN

Extract Content from a File

$ cat uwsgi.log | grep error

Display Contents of All Files in the Current Directory

$ grep . *
$ grep . *.html

List Used Ports

$ netstat -a

# TCP
$ netstat -ntlp | grep uwsgi

# UCP
$ netstat -nulp

Ping a Port

$ curl -I "10.148.70.84:9200"
$ curl -I "192.168.100.10:80"

$ sudo apt-get install nmap
$ nmap -p 4505 54.250.5.176
$ nmap -p 8000 10.10.100.70
$ nmap -p 5672 10.10.100.82

$ telnet 54.250.5.176 4505

ref:
http://stackoverflow.com/questions/12792856/what-ports-does-rabbitmq-use

Show Network Traffic and Bandwidth

$ tcpdump -i eth0

$ sudo apt-get install tcptrack
$ tcptrack -i eth0

ref:
http://askubuntu.com/questions/257263/how-to-display-network-traffic-in-terminal

List Running Processes

# show all processes
$ pstree -a

# also show pid
$ pstree -ap

# 列出前 10 個最佔記憶體的 processes
$ ps aux | sort -nk +4 | tail

# 列出 mysql 相關的 processes
$ ps aux | grep 'worker process'
$ ps aux | grep uwsgi

# 樹狀顯示
$ ps auxf

# 搜尋 process 並以樹狀結果顯示 parent process
$ ps f -opid,cmd -C python

Kill Processes

# 列出目前所有的正在記憶體當中的程序
$ ps aux

# 匹配字串
$ ps aux | grep "mongo"

# 幹掉它
$ kill PID

# kill all processes matching a name
$ sudo pkill -f runserver

Store User's Input as a Variable

$ read YOUR_VARIABLE_NAME

$ read name
# you type: vinta

$ echo $name
vinta

ref:
https://canred.blogspot.tw/2013/03/read.html

Show Terminal Size

$ stty size
$ echo $LINES && echo $COLUMNS
59 273 

ref:
https://stackoverflow.com/questions/263890/how-do-i-find-the-width-height-of-a-terminal-window

File descriptors:

• 0: stdin
• 1: stdout
• 2: stderr

# redirect stdout to a file `test.log`
$ strace uptime > test.log
$ strace uptime 1> test.log

# redirect stderr to a file `test.log`
$ strace uptime 2> test.log

# redirect stderr to stdout
# &1 references the value of the file descriptor 1 (stdout)
$ sh /home/vinta/do_shit.sh > /tmp/do_shit.log 2>&1

# `2> 1` actually means that you redirect stderr to a file named `1`
$ sh /home/vinta/do_shit.sh > /tmp/do_shit.log 2> 1
$ cat 1

# redirect both stderr and stdout to file `test.log`
$ strace uptime &> test.log

# run a command in backgroud
$ long-running-command &

ref:
http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-3.html
https://www.cyberciti.biz/faq/redirecting-stderr-to-stdout/
https://www.brianstorti.com/understanding-shell-script-idiom-redirect/