Question

I have a crontab that looks like

0 0 * * * pg_dump DB_NAME > /path/to/dumps/`date +%Y%m%d`.dmp 

which works fine when I run it manually, but not when cron runs it. After digging through the logs, I see

Dec 12 00:00:01 localhost crond[17638]: (postgres) CMD (pg_dump DB_NAME > /path/to/dumps/`date +) 

It looks like a problem with percent signs, but the man page doesn’t even contain the percent character at all, so I thought they were alright.

Answer 1

You have to escape percent signs with a backslash:

0 0 * * * pg_dump DB_NAME > /path/to/dumps/`date +\%Y\%m\%d`.dmp 

From man 5 crontab:

The ‘‘sixth’’ field (the rest of the line) specifies the command to be run. 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. There is no way to split a single command line onto multiple lines, like the shell’s trailing ‘\’.