Save your time, have these linux commands in your cheatsheet!

🐚 I describe Shell with words omnipresence or has ubiquity. Quick filtering or command chaining is like magic and gives us more powers, with Pipe (”|”) and CLI utilities like sed, awk, grep, etc.

📓 Hence, if you are related to Linux and Server troubleshooting in any way, and that involves your day to day work. Here is some quick reference to command-line know-hows:

Note: This is Part 1, just a quick reference guide that I’ve had in my cheatsheet for server troubleshooting. The list I have is exhaustive, so I will keep things simple and continue to share insights in a phased-out manner.

💡 Command-line | Part 1

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ps | SSH | Removing files | Grep | Find | Sudo | SSL
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Quick reference: PS | SSH | Removing files | Grep | Find | Sudo | SSL

# ps(processes status)

1. Print All Processes Running as Root

   ps -U root -u root

2. Show process tree of all PIDs

   ps auxwf

3. Show all process info and hierarchy

   ps -efH

4. Sort by the highest CPU utilization in ascending order

   ps -aux --sort -pcpu | less

5. Sort by the highest Memory utilization in ascending order

   ps -aux --sort -pmem | less

6. Find top running processes by highest memory and CPU usage in Linux

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

   or

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

7. Sort by memory | CPU and display only the top ten of the result

   ps -aux --sort -pcpu,+pmem | head -n 10

# SSH

Generate generic ssh key pair

ssh-keygen -q -t rsa -f ~/.ssh/<name> -N '' -C <name>

# Removing files

1. Remove files over 30 days old

   find . -mtime +30 | xargs rm -rf

2. Remove files older than 7 day starting with ‘backup’

   find . -type f -name "backup*" -mtime +7 -exec rm {} \;

# Grep

1. Look through all files in current dir for word “foo”

   grep -R "foo” .

2. View last ten lines of output

   grep -i -C 10 "invalid view source” /var/log/info.log

3. Display line number of message

   grep -n “pattern” <file>

# Find

Exclude directories in find

find /tmp -not \( -path /tmp/dir -prune \) -type p -o -type b

# Sudo

To check sudo access for a user!

1. Method 1:

   sudo -l -U sachcode 
   User sachcode may run the following commands on host:(ALL) ALL

2. Method 2: Another way to find out if a user has sudo access is by checking if the said user is member of the sudo group.

   groups sachcode
   sachcode : sachcode wheel docker

3. Method 3: list all sudo users of your system

   genet group sudo

# SSL

With curl's insecure option we can filter the output and get only the Server certificate information:

~ $ curl --insecure -v https://www.sachcode.com 2>&1 | \
> awk 'BEGIN { cert=0 } /^\* Server certificate:/ { cert=1 } \
>  /^\*/ { if (cert) print }'

* Server certificate:* 	subject: CN=*.sachcode.com
* 	start date: Mar 22 04:34:05 2020 GMT
* 	expire date: Jun 20 04:34:05 2020 GMT
* 	common name: *.sachcode.com
* 	issuer: CN=Let's Encrypt Authority X3,O=Let's Encrypt,C=US
* Connection #0 to host www.sachcode.com left intact

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You can read this on dev.to as well!