Cron job isn't writing to log file

Question

I have a shell script that writes the date to a log file when executed. When I run the script manually, the correct output gets written to the file. However, this needs to be automated, and when I run as a cron job, nothing is getting written to the file and I am confused why.

crontab:

0 * * * * tomcat /usr/bin/sh /apps/rdsreplication/snap_replication.sh

Sample Code:

#/bin/bash/

echo ---------------------------------------- >> create_snap.txt
echo Start time:  >> create_snap.txt
date >> create_snap.txt

Any help would be appreciated!

@thrig, this is the crontab for the tomcat user, so I assume it is running out of /home/tomcat/. — AndG, Mar 02 '17 at 17:10
@roaima yes, on this server I ran which sh, and that was the path returned. I am using the tomcat user's crontab, I am adding the line using crontab -e. /var/log/cron shows this: Mar 1 18:06:01 sonar CROND[1585]: (tomcat) CMD (/usr/bin/sh /apps/rdsreplication/snap_replication.sh) — AndG, Mar 02 '17 at 17:13
@roaima: many systemd-based distros have /bin as a symlink to /usr/bin nowadays, since it is no longer possible to have /usr on a separate partition anyway. — Ulrich Schwarz, Mar 02 '17 at 17:19
@UlrichSchwarz I was thinking of Solaris (not used it for years, though) — Chris Davies, Mar 02 '17 at 17:19
@roaima maybe. But what directory is that? NULL on account of Active Directory doing lord knows what? Flapping between what LDAP is providing and a local account, depending on the whims of sssd or such? — thrig, Mar 03 '17 at 15:30
@thrig I don't seem to have any problems with sssd. In the configurations I use there's a template definition for users' home directories so it doesn't need to be specified in AD. However, regardless of how a user's home directory is set up, that's where the cron instance sits. It's up to the user (or sysadmin) to decide whether or not the directory should be writeable. — Chris Davies, Mar 03 '17 at 15:37

score 5 · Accepted Answer · answered Mar 02 '17 at 17:23

The shell script needs to use the full path for the log file:

#/bin/bash/
# assuming you want the txt file in the same directory as the bash script
logfile="$(dirname "$0")/create_snap.txt"
{
    echo ----------------------------------------
    echo Start time:
    date 
} >> "$logfile"

score 1 · Answer 2 · answered Mar 02 '17 at 17:15

1

For a user crontab, the man page for crontab(5) describes the fields:

Each line has five time and date fields, followed by a user name if this is the system crontab file, followed by a command.

So in your case, you'd want this:

0 * * * * /usr/bin/sh /apps/rdsreplication/snap_replication.sh

You should be aware that cron will email you the output and stderr from the job (if any), so you probably have quite a lot of emails telling you that cron can't find the command tomcat. (Or if it can, that tomcat doesn't understand the rest of the line.)

answered Mar 02 '17 at 17:15

Chris Davies

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I tried this, but the date is still not getting written to the log file. I am assuming this is because it is running out of /home/tomcat/ and not /apps/rdsreplication/ where the log file resides? I think if I add this line to the script it should work: cd /apps/rdsreplication/. – AndG Mar 02 '17 at 17:18
1

@N.M.D I haven't seen your script or your system's setup so I can't comment on good locations to run the script from. The cron entry will be run from the user acccount's home directory, so if the script can't run from there it needs to change directory - or you need to use cd /correct/path && sh /apps/.../snap_replication.sh. – Chris Davies Mar 02 '17 at 17:24

Cron job isn't writing to log file

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