Linux #

Set a static IP for a network card on AWS Linux/Centos #

File: /etc/sysconfig/network-scripts/ifcfg-eth0

HWADDR=<MAC_ADDRESS>
TYPE=Ethernet
BOOTPROTO=none // turns off DHCP
IPADDR=192.168.2.2 // set your IP
PREFIX=24 // subnet mask
GATEWAY=192.168.2.254
DNS1=1.1.1.2 // set your own DNS
DNS2=1.0.0.2
DNS3=9.9.9.9
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
NAME=eth0
DEVICE=eth0
ONBOOT=yes // starts on boot

Set a dynamic IP for a network card on AWS Linux/Centos #

File: /etc/sysconfig/network-scripts/ifcfg-eth0

HWADDR=<MAC_ADDRESS>
TYPE=Ethernet
BOOTPROTO=dhcp
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
NAME=eth0
DEVICE=eth0
ONBOOT=yes // starts on boot

Set global DNS/Gateway on AWS Linux/Centos #

File: /etc/sysconfig/network

GATEWAY=

View current DNS server address #

cat /etc/resolv.conf

View current Gateway #

ip route | grep default

Ifconfig shows ens instead of eth #

Icfg files are not picked up by their MAC address!
Name the files as ifcfg-ens33
Remove the mac address from ifcfg files
Set the DEVICE in ifcfg to ens33

Change hostname #

For non AWS Linux #

To view current hostname

hostname

To change hostname

nano /etc/hostname

nano /etc/hosts

Change hostname on AWS Linux #

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/set-hostname.html

Restart the linux networking service #

service network restart or sudo systemctl restart network

Check if network port is open on Linux #

echo > /dev/tcp/google.com/80 && echo "Port is open"

Install redis on AWS linux #

sudo yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
sudo yum install https://rpms.remirepo.net/enterprise/remi-release-7.rpm
sudo yum --enablerepo=remi install redis
sudo nano /etc/redis/redis.conf

Comment line “ bind 127.0.0.1 -::1”
Change protected-mode to no

sudo chkconfig redis on
sudo service redis restart

Install nvm on linux #

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.1/install.sh | bash

Zip on linux #

zip -r destination.zip sourceDir

Unzip on linux #

unzip filename.zip -d /path/to/directory

Time how long a command takes on linux #

time <command>

Disable firewall on linux #

sudo systemctl stop firewalld
sudo systemctl disable firewalld

Yum - updates commands #

Install all updates using yum
- yum update
List packages to update using yum
- yum check -updates
List installed updates using yum
- sudo yum history
- OR sudo cat /var/log/yum.log
Undo/rollback/revert an installed update using yum
- yum undo <transaction_id>
Install only security updates using yum
- yum update --security
Install only bug fixes using yum
- yum update --bugfix
Update specific package using yum
- yum upgrade <package>

View details about a running process on Linux #

ps -p <PROCESSID> -o pid,vsz=MEMORY -o user,group=GROUP -o comm,args=ARGS

Find files of specific extension on Linux #

find . -type f -name "*.html"

Copy files of specific extension on Linux #

find . -type f -name "*.html" -exec cp --parents {} ./destination \;

Find a string in multiple files on Linux #

grep -rn '/path/to/somewhere/' -e 'pattern'
- -r or -R is recursive,
- -n is line number, and
- -w stands for match the whole word.
- -l (lower-case L) can be added to just give the file name of matching files.
- -e is the pattern used during the search
- Along with these, --exclude, --include, --exclude-dir flags could be used for efficient searching:
Exclude a directory from find
- grep -rn '/path/to/somewhere/' -e 'pattern' --exclude-dir testdir

Convert EOL/EOF line endings for entire directory #

On a linux machine (or WSL) install dos2linux
- sudo apt install dos2unix
- find . -type f -name '*.ts' -print0 | xargs -0 dos2unix
The same applies to the unix2dos

View free memory on Freebsd #

dmesg | grep memory
free -m

Mysql settings file (for changing memory settings) #

etc\my.cnf

Block an IP address on Linux #

iptables -A INPUT -s IPADDRESS -j DROP
http://www.cyberciti.biz/faq/how-do-i-block-an-ip-on-my-linux-server/

Block a subnet on Linux #

iptables -A INPUT -s IPADDRESS/SUBNET -j DROP

i.e. sudo iptables -A INPUT -s 183.181.204.0/255.255.255.0 -j DROP

Remove a rule from IP tables on Linux #

Same as add but with -D instead of -A
iptables -D INPUT -s IPADDRESS -j DROP

List ip table rules on Linux #

sudo iptables -S

View high CPU processes on Linux #

top

To modify the output of top command
- Type ‘i’ to remove the idle processes from the display.
- To revert back type ‘i’ again.
- To sort the data by memory usage type ‘M’
- To sort by how long the processes have been running type ‘S’ and type ‘P’ to sort by CPU usage again.
- It is also possible to modify the processes from within the top command.
- Type ‘u’ to view processes owned by a specific user
- Type ‘k’ to kill processes and ‘r’ to renice them.
%CPU column – CPU Usage
- The percentage of your CPU that is being used by the process.
- By default, top displays this as a percentage of a single CPU.
- On multi-core systems, you can have percentages that are greater than 100%. For example, if 3 cores are at 60% use, top will show a CPU use of 180%. - You can toggle this behavior by hitting Shift-i while top is running to show the overall percentage of available CPUs in use.

References

Give full access to a file on Linux #

chmod 777 <FILE>
chmod -R 777 <DIR>

Change owner on Linux #

chown user <FILE>
chown user:group <FILE>
chown -R user:group <DIR>

Find apache current dir on Linux #

httpd -V

Find last boot time on Linux #

who -b

View Path on linux #

echo $PATH

How to get the size of a directory on linux #

du -sh <DIR>

How to get the size of current files and subdirectories on linux #

du -sh ./*

su - USERNAME

Linux Tips/Cheat sheets #

Learn Linux (fast): 30 commands for beginners (with cheat sheet) - from hackthebox.com

Linux networking commands #

Linux networking commands
by Julia Evans

View current Amazon Linux version #

cat /etc/os-release

grep -E -w 'VERSION|NAME|PRETTY_NAME' /etc/os-release

Remi RPM repository installation instructions #

https://rpms.remirepo.net/wizard/

Remove an RPM repository (CENTOS 7) #

Find the exact installed repo name
rpm -qa | grep epel
Remove it
sudo yum remove epel-release-7-14.noarch

Instal httrack on fedora/centos amazon linux #

Download the latest linux sources version of httrack (https://www.httrack.com/page/2/)
tar xvf <downloaded-file>.tar.gz
sudo yum install openssl-devel zlib-devel
sudo yum groupinstall "Development Tools"
Move to the directory containing the source of httrack
./configure
make
sudo make install

Extend disk space inside a linux vm after vmware host disk resize #

To resize a partition, you actually “delete” it and then add a new one with the new size, making sure to place the beginning of the new partition at the same sector/cylinder as the old one started. This process is NOT destructive, your data still remains on the disk. These first steps are for deleting the partition:

The fdisk command provides disk partitioning functions and using it with the -l switch lists information about your disk partitions. At the command prompt type fdisk -l
The response should say something like Disk /dev/sda : xxGB
At the command prompt type fdisk /dev/sda. (if dev/sda is what was returned )
Type p to print the partition table and press Enter
Type d to delete the last partition
Type the number of the last partition
Type n to add a new partition
Type p again to make it a primary partition
Now you’ll be prompted to pick the first cylinder which will most likely come at the end of your last partition
If you want it to take up the rest of the space available, just choose the default value for the last cylinder.
Type w to save these changes
Restart the VM
pvresize /dev/sda2
lvextend -r -l +100%FREE /dev/mapper/centos-root

Work with multiple terminals in linux using ‘screen’ #

Screen is used to create a new ‘screen’ session, each screen session can have multiple windows

Start a screen session: screen
List all screen sessions: screen -ls
Connect to a screen session: screen -r <ID>
Detach from a screen session: Ctrl+D
While in a screen session
- Create a new window: Ctrl+A C
- List all windows and switch between them: Ctrl+A "
- Create a split: Ctrl+A S
- Switch between splits: Ctrl+A Tab
- Remove current split: Ctrl+A Q

Permissions #

Binary, Octal, String Representation, and Permissions #

Binary	Octal	String Representation	Permissions
000	0	—	No Permission
001	1	–x	Execute
010	2	-w-	Write
011	3	-wx	Write + Execute
100	4	r–	Read
101	5	r-x	Read + Execute
110	6	rw-	Read + Write
111	7	rwx	Read + Write + Execute

Example #

Owner	Group	Other
rwx	rw-	r-x

Example Owner Permissions Breakdown #

Permission	Symbol	Value	Total
Read	r	4
Write	w	2	7
Execute	x	1

Example Group Permissions Breakdown #

Permission	Symbol	Value	Total
Read	r	4
Write or Edit	w	2	6
No Permission	-	0

Example Other Permissions Breakdown #

Permission	Symbol	Value	Total
Read	r	4
No Permission	-	0	5
Execute	x	1

Log Parsing Commands #

From ByteByteGo

GREP
`$grep<pattern>file.log`	1.	find file names that match	`$grep -l"bytebytego" *.log`	4.	invert matches	`$grep -v"bytebytego" test.log`
GREP searches any given input files, selecting lines that match one or more patterns	2.	case insensitive word match	`$grep -wi"bytebytego" test.log`	5.	take patterns from a file	`$grep -f pattern.txt test.log`
	3.	show line numbers	`$grep -n"bytebytego" test.log`	6.	search recursively in a dir	`$grep -R"bytebytego"/home`

CUT
`$cut -d", " -f 3 file.log`	1.	cut first 3 bytes	`$cut -b 1,2,3 file.log`	3.	specify characters position	`$cut -c 1-8 test.log`
CUT cuts out selected portions of each line from each file and writes them to the standard output	2.	select 2nd column delimited by a space	`$cut -d" " -f 2 test.log`

SED
`$sed s/<regex>/<replace>/g`	1.	substitute a string	`$sed s/bytebytego/go/g test.log`	4.	replace string on a range of lines	`$sed '2-4 s/bytebytego/go/' test.log`
SED reads the specified files, modifying the input as specified by a list of commands	2.	replace the 2nd occurrence	`$sed s/2/bytebytego/go/2 test.log`	5.	delete a line	`$sed '4d' test.log`
	3.	replace string on the 4th line	`$sed '4 s/bytebytego/go/' test.log`

AWK
`$awk{print $4} test.log`	1.	print matched lines	`$awk '/bytebytego/ {print}' test.log`	4.	print lines with more than 10 characters	`$awk 'length($0)>10' test.log`
AWK scans each input file for lines that match any of a set of patterns	2.	split a line into fields	`$awk '{print $1,$3}' test.log`	5.	find a string in a column	`$awk '{if($4=="byte" print $0;}' test.log`
	3.	print lines 2 to 7	`$awk 'NR>=2, NR<=7' (print NR, $0)' test.log`

SORT
`$sort test.log`	1.	output to a file	`$sort -o output.txt input.txt`	4.	sort based on the 3rd column	`$sort -k 3n test.log`
SORT sorts text and binary files by lines	2.	sort in reverse order	`$sort -r test.log`	5.	check if a file is ordered	`$sort -c test.log`
	3.	sort numerically	`$sort -n test.log`	6.	sort and remove duplicates	`$sort -u test.log`

UNIQ
`$uniq test.log`	1.	tell how many times a line is repeated	`$uniq -c test.log`	4.	skip the first two fields	`$uniq -f 2 test.log`
UNIQ reads the specified input file comparing adjacent lines, and writes a copy of each unique input line to the output file	2.	print repeated lines	`$uniq -d test.log`	5.	compare case-insensitive	`$uniq -i test.log`
	3.	print unique lines	`$uniq -u test.log`

Retry a commands in shell scripts #

for i in {1..5}; do n 18 && break || sleep 15; done

Convert file contents to base64 #

 base64 -w 0 "<INPUT_FILE>" > "<OUTPUT_FILE>"