supervisor and cron commands

Supervisor And Cron

#########################
Supervisor
#########################


First install supervisor
apt install supervisor

Create a program then give permission to program
chmod +x <program_path>


The program configuration files for Supervisor programs are found 
in the /etc/supervisor/conf.d directory

create conf file for your program

/etc/supervisor/conf.d/<new_file>.conf

add the following details

[program:<give_a_name>]
command=<program_path>
autostart=true
autorestart=true
stderr_logfile=<log_file_path_1>
stdout_logfile=<log_file_path_2>


For example
log_file_path_1 can be /var/log/long.err.log


Now run the following commands

supervisorctl reread

supervisorctl update

Now supervisor will start supervising the configured program

You can enter interactive shell by typing 

supervisorctl

start all configuration
supervisorctl start all

stop all configuration
supervisorctl stop all



#########################
Cron
#########################

First install cron
apt install cron

To edit crontab 
crontab -e

To view the crontab
crontab -l

To remove the crontab
crontab -r

* * * * * <file_path> 1>/dev/null 2>&1

minute
hour
day of the month
month
day of the week

@hourly - Shorthand for 0 * * * *
@daily - Shorthand for 0 0 * * *
@weekly - Shorthand for 0 0 * * 0
@monthly - Shorthand for 0 0 1 * *
@yearly - Shorthand for 0 0 1 1 *
@reboot, which runs the command once at startup.

*	any value
,	value list separator
-	range of values
/	step values

To run command everyday at 9pm (21:00)
0 21 * * * sample.sh 1>/dev/null 2>&1

To run sample.sh every Tuesday to Saturday at 1am (01:00)
0 1 * * 2-7 command 1>/dev/null 2>&1

To run sample.sh at 07:30, 09:30 13:30 and 15:30
30 07,09,13,15 * * * sample.sh

The files for each user are located at /var/spool/cron/crontab, 
but they are not supposed to be edited directly.
Instead, it's best to use the crontab command.


################day of week vs day of month#################

Going back a step further from Vixie cron, the "wday OR mday" 
logic was present in System V cron, but not System III or anything earlier.

Before Paul Vixie wrote his cron replacement, BSD cron was like the
SysIII-and-earlier cron. All 5 fields were ANDed. The post-4.4 BSDs 
adopted Vixie cron, making themselves more SysV-like.

So don't ask (blame) Vixie. He was just cloning SysV.