Tar crontab not working, while command works on it's own

Question

I have this crontab

* * * * * tar -czf /backup/$(date +%F--%T)-localusers.tgz /vagrant

It does not work. But if I do

tar -czf /backup/$(date +%F--%T)-localusers.tgz /vagrant/

It works.

Anybody have a clue what's going on? I do keep getting a mail though:

N 10 (Cron Daemon) Thu Aug 23 10:43 28/1130 "Cron <root@localhost> tar -czf"

See the answer there that talks about % in crontabs. – Jeff Schaller Aug 23 '18 at 14:49 — Jeff Schaller, Aug 23 '18 at 14:49
... or How can I execute date inside of a cron tab job? – steeldriver Aug 23 '18 at 14:51 — steeldriver, Aug 23 '18 at 14:51

score 1 · Accepted Answer · answered Aug 23 '18 at 14:51

1

Your problem is likely because of the cron special treatment of percent sign:

The entire command portion of the line, up to a newline or % character, will be executed by `/bin/sh or by the shell specified in the SHELL variable of the crontab file. Percent-signs (%) in the command, unless escaped with backslash (), will be changed into newline characters, and all data after the first % will be sent to the command as standard input.

So you need to escape them:

* * * * * tar -czf /backup/$(date +\%F--\%T)-localusers.tgz /vagrant

answered Aug 23 '18 at 14:51

weirdan

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Would it be bad if I changed the shell that crontab uses into /bin/bash? Would I break anything? – iamAguest Aug 23 '18 at 14:58
It would only affect you particular crontab, so it should be fairly safe. Of course you would still need to escape percent signs, as those are processed before the command line is handed out to shell (whatever that shell may be). – weirdan Aug 23 '18 at 15:00

Tar crontab not working, while command works on it's own

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