In some cases it makes sense to run a cronjob with an output file containing the current date (e.g. a backup file).
In my case I needed to get the content of a website every 30 minutes and save the content to an output file.
Here's my crontab entry:
30 * * * * wget http://www.example.com/myscript.php -O /tmp/output-$(date +%Y%m%d%H%M).out
Unfortunately that didn't work and resulted in the following error (seen in /var/log/cron.log):
/USR/SBIN/CRON: (web0) CMD (wget http://www.example.com/myscript.php -O /tmp/output-$(date +)
/USR/SBIN/CRON: (CRON) error (grandchild #28734 failed with exit status 1)
The interesting part here is that the date format (+%Y%m%d%H%M) is not shown in the log entry. Why's that?
On my research I came across a very interesting article (http://www.alleft.com/sysadmin/common-cron-mistakes), which basically reminded me of the following importance:
The first important observation about the crontab file is this: It’s not a shell script.
Facepalm. Of course! I got too used to create a shell script and then execute this shell script in the crontab. Here I want the final commands directly launched from cron.
In the same article an important information is also given, that percentage signs (%) need to be escaped in a crontab file. Let's verify this.
First a standard echo of the current year:
01 * * * * /bin/echo $(/bin/date '+%Y') >> /tmp/test.log
This failed - actually not a big surprise because I ddin't escape the percentage sign:
/USR/SBIN/CRON: (root) CMD (/bin/echo $(/bin/date '+)
/USR/SBIN/CRON: (CRON) error (grandchild #30113 failed with exit status 1)
Now let's try the same with the escaped percentage:
02 * * * * /bin/echo $(/bin/date '+\%Y') >> /tmp/test.log
/usr/sbin/cron: (root) RELOAD (crontabs/root)
/USR/SBIN/CRON: (root) CMD (/bin/echo $(/bin/date '+%Y') >> /tmp/test.log)
That looks much better! Let's verify the output:
Success! Let's hope that having written it down now will remind me quicker next time.
No comments yet.
AWS Android Ansible Apache Apple Atlassian BSD Backup Bash Bluecoat CMS Chef Cloud Coding Consul Container Containers CouchDB DB DNS Database Databases Docker ELK Elasticsearch Filebeat FreeBSD Galera GlusterFS Grafana Graphics HAProxy HTML Hacks Hardware Icinga Icingaweb2 InfluxDB Internet Java KVM Kibana Kodi Kubernetes LTS LXC Linux Logstash Mac Macintosh Mail MariaDB Minio MongoDB Monitoring Multimedia MySQL NFS Nagios Network Nginx OSSEC OTRS Office PGSQL PHP Perl Personal PostgreSQL Postgres PowerDNS Proxmox Proxy Python Rancher Redis SSL Samba Seafile Security Shell SmartOS Solaris Surveillance SystemD Systemd TLS Tomcat Ubuntu Unix VMWare VMware Varnish Virtualization Windows Wireless Wordpress Wyse ZFS Zoneminder