I want to view the all cron jobs in linux. Whats the command
varies by distro, varies by cron software, varies by usage.
this should cover everything on rhel/centos/fedora:
/etc/crontab /etc/cron.d/* /etc/cron.daily/* /etc/cron.hourly/* /etc/cron.monthly/* /etc/cron.weekly/* /var/spool/cron/*
As root, you can use the -u parameter to crontab mixed with -l to view that users crontab entries. Something like this:
cat /etc/passwd |cut -d ":" -f 1 | while read narf; do crontab -u $narf -l; done
That will get every username in your passwd file -- grabbing the first field (-f 1) using ':' as a delimiter (-d ":") with cut, and then calling crontab -u -l for each user in the passwd file.
Often there is also a file /etc/crontab with the system-wide jobs.
In order to be complete, we mustn't forget anacron: