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Im pretty new to unix and crons, I was currently about to try to add crons to an existing cron file. I read you could do this with crontab -e. The confusing thing to me is just that crontab -e shows different crons/commands than less /etc/crontab - how come? Which one is the correct way/file to edit?

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2 Answers 2

up vote 3 down vote accepted

Although @X Tian's answer contains info on the different files for crontab, the essential information concerning your question is this:

crontab -e edits the user's crontab file (stored in the /var/spool/cron/crontabs/ directory on current Debian systems, but YMMV) or creates a new one, and not /etc/crontab. Similar for crontab -l (list crontab file) and crontab -r (remove crontab file).

For all cron jobs that should be executed under a user's account, you should use crontab -e. For system jobs, you should add a file under /etc/cron.d, if that exists; under /etc/cron.{hourly|daily|weekly|monthly} (but those must not be named like a package name!), if that fits your purpose; or add a line to /etc/crontab. But be aware that /etc/crontab might be overwritten with a system update.

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@Stephane Chazelas Thank you for clarifying with your edit. The /var/spool/cron/ directory is a Linux specialty (see the File Hierarchy Standard) and the location may vary on systems other than a current Debian. –  Dubu Mar 13 at 14:47
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You really want to read the manual pages man cron and man crontab

Here is an extract which covers your question. From man cron

NOTES cron searches its spool area (/var/spool/cron/crontabs) for crontab files (which are named after accounts in /etc/passwd); crontabs found are loaded into memory. Note that crontabs in this directory should not be accessed directly - the crontab command should be used to access and update them.

   cron also reads /etc/crontab, which is in a slightly  different  format
   (see  crontab(5)).   Additionally, cron reads the files in /etc/cron.d:
   it treats  the  files  in  /etc/cron.d  as  in  the  same  way  as  the
   /etc/crontab  file  (they  follow the special format of that file, i.e.
   they  include  the  user  field).  However,  they  are  independent  of
   /etc/crontab:  they  do  not, for example, inherit environment variable
   settings from it. The intended purpose of  this  feature  is  to  allow
   packages  that  require  finer  control  of  their  scheduling than the
   /etc/cron.{daily,weekly,monthly} directories to add a crontab  file  to
   /etc/cron.d. Such files should be named after the package that supplies
   them. Files must conform to the same naming convention as used by  run-
   parts(8):  they  must  consist solely of upper- and lower-case letters,
   digits, underscores, and hyphens. If the -l option is  specified,  then
   they must conform to the LSB namespace specification, exactly as in the
   --lsbsysinit option in run-parts.
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You should specify which cron implementation and which version thereof on which OS and which version thereof you're quoting that from. cron is something that varies a lot from OS to OS and on some you can choose between several implementations. –  Stéphane Chazelas Mar 13 at 12:59
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