ls

ls -l

Display the contents of the current directory

ls -a

ls -ltr

ls -ld /lib/*/

Display also hidden files and hidden directories

Order files by last modified date

Directories only

cp filename /path/dir_name

Copy filename into directory /path/dir_name

cp -r dir_name /path/dir_name2

Copy the entire dir_name into /path/dir_name2

cp filename1 filename2 /path/dir_name

Copy filename1 and filename2 into /path/dir_name

rm name

Remove a file or directory called name

rm -r name

Remove an entire directory as well as its included files and subdirectories

 find /home/modelsig/mail/new -type f -delete

 Remove a ton of files to get around "too many arguments" problem

mv filename /path/dir_name

Move filename into /path/dir_name

mv filename1 filename2

Rename filename1 to filename2

cat filename

Display filenames contents

more filename

Display filename in pages. Use spacebar to view next page

head filename

Display filenames first 10 lines

head -15 filename

Display filenames first 15 lines

tail filename

Display filenames last 10 lines

tail -15 filename

Display filenames last 15 lines

tail -f myfile.txt

pwd

Display current directory

cd /path/dir_name

Change to directory /path/dir_name

cd ..

Go 1 directory up

mkdir dir_name

Create directory dir_name

rmdir dir_name

Delete directory dir_name

updatedb

Update (create first time used) a database of all files under the root directory /

locate filename

locate crontab

Find file filename searching in the database

All files that contain the word crontab

find / -name filename

Starting from the root directory search for the file called filename

find / -name *filename

find -iname "MyCProgram.c"

find -iname "MyCProgram.c" -exec md5sum {} \;

Same as above but search for file containing the string filename

Case insensitive find

Execute command on files found

grep string /path/dir_name

grep -i "the" demo_file

grep -A 3 -i "example" demo_text

grep -r "ramesh" *

Starting from /path/dir_name search for all files containing string

Case-insensitive

Print matched line + 3 lines after

Search for a given string in all files recursively

which application_name

Search $path for application app_name

whereis application_name

Search $path, man pages and source files for application_name

tar -xzf filename.tgz

Decompress tzg file

tar -xzf filename.tar.gz

Decompress tar.gz file

tar -xjf filename.tar.bz2

Decompress tar.bz2 file

tar -czf filename.tar /path/dir_name

Compress directory /path/dir_name to filename.tar

tar -czvf compressed_file.tar.gz file1.txt file2.jpg

Compress multiple files

gzip -c filename > filename.gz

Compress /path/dir_name to filename.tar.gz

bzip2 -c filename > filename.bz2

Compress /path/dir_name to filename.tar.bz2

rpm -hiv package.rpm

Install rpm called package.rpm

rpm -hiv --force package.rpm

Install rpm called package.rpm by force

rpm -hUv package.rpm

Upgrade rpm called package.rpm

rpm -e package.rpm

Delete rpm called package.rpm

rpm -qpil package.rpm

List files in not-installed rpm called package.rpm

rpm -ql package.rpm

List files in installed rpm called package.rpm

rpm -q str

List installed rpms containing the string str

rpm -qf /path/application_name

Display the rpm that contains application application_name

startx

Start the X system

shutdown -h now

Shutdown the system now and do not reboot

halt

Same as above

shutdown -r now

Reboot

reboot

Same as above

shutdown -r +10

Reboot in 10 minutes

shutdown -c

Cancel a pending shutdown

at 3:00 AM tomorrow
at> echo "shutdown -r now"
ENTER
Control-D

atq (to display the queue)
atq
434     Fri Nov  9 15:25:00 2018 a root

atrm deletes jobs, identified by their job number.
atrm 434

 Schedule a reboot using the at command.

The at command schedules a command to be run once at a particular time that you normally have permission to run. The at command can be anything from a simple reminder message, to a complex script. You start by running the at command at the command line, passing it the scheduled time as the option. It then places you at a special prompt, where you can type in the command (or series of commands) to be run at the scheduled time. When you're done, press Control-D on a new line, and your command will be placed in the queue.

$ at now + 1 minutes
at> echo "Hello Fido" > test.txt

at 9:30 PM Tue
at noon
at midnight
at tomorrow (24 hrs. from now)
at 2:30 PM tomorrow
at 2:30 PM 10/21/2014

/etc/init.d/mysqld start
/etc/init.d/mysqld stop
/etc/init.d/mysqld restart

service mysqld start
service mysqld stop
service mysqld restart

service mysql start
service mysql stop
service mysql restart

mount -t vfat /dev/sd(a)(1) /mnt/c_drive

Mount the first partition 1 of the first hard disk drive a which is in fat32 vfat dormat under /mnt/c_drive directory

mount -t iso9660 /dev/cdrom /mnt/cdrom

Mount cdrom under /mnt/cdrom directory

umount /mnt/hda1

Unmout the above

users

Display users currently logged in

adduser username

Create a new user called username

passwd username

Define password for user called username

who

List logged-in users

whoami

Display current user

finger username

Displays info about user username

su

Log in as root from current login

su -

Log in as root from current login and take root's path

exit

Exit from console login (ie, logout).

command

Execute command in the foreground

command &

Execute command in the background

ctrl+z

Suspend a program

ctrl+c

Interrupt a program

ps

List all processes

kill -9 pid

Kill process with id pid

top

Monitor processes in real time

hostname

List the system's hostname

ifconfig

Set/Display network information

host ip

Resolves ip's hostname

ping ip/hostname

Check if ip/hostname is reachable

traceroute ip/hostname

Find network path to ip/hostname

uname -a

General system information

fdisk -l

List partition tables

cp filename /path/dir_name

Copy filename into directory /path/dir_name

df -T -h

List filesystem disk space usage

lspci

List PCI devices

lsusb

List USB devices

free -m

Display RAM+Swap usage

gcc -o output file.c

Compile a C program

./output

Run a C program you have compiled

g++ -o output file.cpp

Compile a C++ program

./output

Run a C++ program you have compiled

./configure && make && su -c 'make install'

Configure, compile and install a program with Makefile

https://www.computerhope.com/unix/ucrontab.htm
https://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/
https://serverfault.com/questions/801257/should-i-edit-etc-crontab-or-run-crontab-e-as-root
https://www.thegeekstuff.com/2009/06/15-practical-crontab-examples

https://www.perl.com/article/43/2013/10/11/How-to-schedule-Perl-scripts-using-cron/

***************************

When you create a crontab file, it is automatically placed in the /var/spool/cron/crontabs directory and is given your user name. You can create or edit a crontab file for another user, or root, if you have superuser privileges.

System crontabs: etc/crontab; etc/cron.daily; etc/cron.weekly; etc.

***************************

LOAD CRONTAB FROM TEXT FILE:
crontab /home/catalyst/icdf/script/cron-file.txt

MAILTO=webmaster@wyoming.com
# First day of every month at 5am:
0 5 1 * * perl /home/catalyst/icdf/script/ContractExpireNotify.pl

-------------------------------------------

ROOT USER:
crontab -l

crontab -u michael.carroll -l
crontab /var/spool/cron/crontabs/www-data
sudo crontab -l -u jeff

Minute - Hour - Day - Month - Day(s) of Week

# Every minute:
* * * * * /home/catalyst/icdf/script/SendMailPerl.pl
# * * * * * /home/catalyst/icdf/script/ContractExpireNotify.pl
#
# Every 10 minutes:
# */10 * * * * /home/ramesh/check-disk-space
#
# Every day at 5am:
# 0 5 * * * /home/catalyst/icdf/script/ContractExpireNotify.pl
#
# Send the job output to a log file:
# 0 8 * * * /usr/local/bin/myjob > /var/log/myjob.log 2>&1

crontab -e
TO EXIT EDITOR:
:x<Enter> quit vi, writing out modified file to file named in original invocation
:wq<Enter> quit vi, writing out modified file to file named in original invocation
:q<Enter> quit (or exit) vi
:q!<Enter> quit vi even though latest changes have not been saved for this vi call

LIST USER CRONTABS:
ls /var/spool/cron
 

VIEW ALL CRONTABS:
more /etc/crontab


VIEW SINGLE USER CRONTAB:
crontab -u johnvinc -l


CRONTAB LOGS:
grep CRON /var/log/syslog
tail -10 /var/log/cron
cat /var/log/cron | grep johnvinc
head -10 /var/log/cron | grep johnvinc

REMOVE CRONTAB:
crontab -u johnvinc -r

RESTART CRON:
/etc/init.d/cron reload

Testing Cron Jobs By Simulating Cron Shell:
https://cronitor.io/docs/cron-troubleshooting-guide

# env -i /bin/sh
# cd ~
# env
PWD=/root

- Then run the script to see if there's a useful error message.

# /usr/local/bin/Libre_ap_report_mail.pl monthly
Can't locate Mail/Sender.pm in @INC (you may need to install the Mail::Sender module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.24.1 /usr/local/share/perl/5.24.1 /usr/lib/x86_64-linux-gnu/perl5/5.24 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.24 /usr/share/perl/5.24 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /usr/local/bin/Libre_ap_report_mail.pl line 6.
BEGIN failed--compilation aborted at /usr/local/bin/Libre_ap_report_mail.pl line 6.

- Exit, then run # env again to see if there is something missing in the bare shell (/bin/sh).

- Might be able to do a fix on scripts like this:

use lib '/root/perl5/lib/perl5';