Making Ruby Scripts work Under System D Using rbenv

This has bit me I think every single time I make a SystemD launch script using ruby and rbenv (RVM is worse; imho). Perhaps writing it down for once makes the lesson stick.

Let's start with our SystemD unit file that doesn't work:

[Unit]
Description=Twitter To Kafka

[Service]
SyslogIdentifier=twitter_to_kafka
User=ubuntu
PIDFile=/home/ubuntu/twitter_to_kafka/twitter_to_kafka.pid
WorkingDirectory=/home/ubuntu/twitter_to_kafka

ExecStart=/home/ubuntu/twitter_to_kafka/twitter_to_kafka.sh
ExecReload=/home/twitter_to_kafka/twitter_to_kafka/twitter_to_kafka.sh
ExecStop=/bin/kill -s QUIT $MAINPID
Restart=always

[Install]
WantedBy=multi-user.target

This generates errors like these:

❯ sudo systemctl status twitter_to_kafka.service
● twitter_to_kafka.service - Twitter To Kafka
   Loaded: loaded (/lib/systemd/system/twitter_to_kafka.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Thu 2020-02-13 12:57:48 UTC; 1min 54s ago
  Process: 7615 ExecStart=/home/ubuntu/twitter_to_kafka/twitter_to_kafka.sh (code=exited, status=203/EXEC)
 Main PID: 7615 (code=exited, status=203/EXEC)

Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: twitter_to_kafka.service: Main process exited, code=exited, status=203/EXEC
Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: twitter_to_kafka.service: Failed with result 'exit-code'.
Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: twitter_to_kafka.service: Service hold-off time over, scheduling restart.
Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: twitter_to_kafka.service: Scheduled restart job, restart counter is at 5.
Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: Stopped Twitter To Kafka.
Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: twitter_to_kafka.service: Start request repeated too quickly.
Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: twitter_to_kafka.service: Failed with result 'exit-code'.
Feb 13 12:57:48 ip-172-31-24-213 systemd[1]: Failed to start Twitter To Kafka.

The problem is that rbenv is a shell extension so the shell has to be loaded to run this correctly. Just adding /bin/bash -lc to ExecStart and ExecReload fixes this. Here's the actual working unit file:

[Unit]
Description=Twitter To Kafka

[Service]
SyslogIdentifier=twitter_to_kafka
User=ubuntu
PIDFile=/home/ubuntu/twitter_to_kafka/twitter_to_kafka.pid
WorkingDirectory=/home/ubuntu/twitter_to_kafka

ExecStart=/bin/bash -lc /home/ubuntu/twitter_to_kafka/twitter_to_kafka.sh
ExecReload=/bin/bash -lc /home/twitter_to_kafka/twitter_to_kafka/twitter_to_kafka.sh
ExecStop=/bin/kill -s QUIT $MAINPID
Restart=always

[Install]
WantedBy=multi-user.target

Sample github file where I found this.