Basic Linux Administration Skills -Part 1/2

These are some of the most recommended skills in a DevOps Engineers.

1.How to start /stop services

Sometimes, there might be instance where we want to view the status of a service or even restart the same and here are a few useful commands for few common services :

All these service works on several scripts and these scripts are stored in /etc/init.d location, this init.d is a daemon which is the first process of the Linux system.

sudo  /etc/init.d/apache stop — Stops the Apache server
sudo /etc/init.d/mysql start — Starts the SQL server 
sudo /etc/init.d/mysql restart — Retarts the SQL server
sudo /etc/init.d/cron status — It can be active(running) or inactive (dead)

2.How to diagnose or fix high loads

There’s at least one server resource (RAM, CPU, I/O, etc.) that’s being abused.

• Using htop command shows you the current running processes and the CPU each process is consuming.
• Crons could be taking high CPU and it can be disabled if it doesn’t ruin the system.

The /proc/ directory — also called the proc file system — contains a hierarchy of special files which represent the current state of the kernel

cat /proc/loadavg to find the average load of CPU and IO
cat /proc/meminfo — To give the memory info.

3. How to diagnose or fix disk space issues

• df -h used to check the Disk Usage and Swap Memory can be enabled if needed
• Delete unwanted files rm <filename> or rm -rf <directory>
• Compress files — gzip <directory>
• Compress files using tar commands —

tar -cf newdirectory.tar directoryold , where -c is create newdirectory.tar from the directory named directoryold

4. How to Setup and Configure Linux Firewalls :

“IPTables” is the default tool provided in Linux to establish a firewall. Iptables is used to set up, maintain and inspect the tables of the IPv4 and IPv6 packet filter rules in the Linux Kernel.

a. List the current rules of iptables:

sudo iptables -L

b. To change the default policy:

sudo iptables -P Chain_name Action_to_be_taken

Example:-

sudo iptables -P FORWARD DROP

c. To append a rule at the end of the chain:

sudo iptables -A

d. To append a rule at the start of the chain:

sudo iptables -I

e. To implement a ACCEPT rule:-

sudo iptables -A/-I chain_name -s source_ip -j action_to_take

Example:-

iptables -A INPUT -s 192.168.1.3 -j ACCEPT

f. Implementing rules on specific ports/protocols:-

sudo iptables -A/-I chain_name -s source_ip -p protocol_name --dport port_number -j Action_to_take

Example:-

sudo iptables -I INPUT -s 192.168.1.3 -p tcp --dport 22 -j ACCEPT

g. To delete a rule:-

sudo iptables -D chain_name rule_number

Example:-

sudo iptables -D INPUT 1

h. To save the configuration:-

sudo invoke-rc.d iptables-persistent save

Here’s a well detailed article on the same.

How to setup firewall in Linux? - GeeksforGeeks

5. How to Install /Update Packages

In Ubuntu, Advanced Package Tool — apt is the package management tool

sudo apt-get install <pkg>or apt-get update <pkg>

In Mac , Homebrew is one of the the package installation tool

brew install <pkg>

Cheers, Linu!