Systemd ExecStart – Troubleshooting Escape Characters Failures

cloud-initJenkinssedsystemd

I have the following snippet to extract a value from a jenkins server jnlp config file. It works out of the box in the terminal but not as a unit. I want a unit so I can put the value somewhere and use it as an environment variable. However I keep getting an escape sequence error. I found this which suggests I only need to worry about quotes and slashes, but I get the same result. Here is the ExecStart of the file with the sed included:

ExecStart=/bin/sh -c 'curl -L -s -X GET http://10.x.x.x:8080/computer/name-of-executor/slave-agent.jnlp | sed \"s/.*<application-desc main-class=\"hudson.remoting.jnlp.Main\"><argument>\([a-z0-9]*\).*/\1/\" >> /etc/build_environment'

I have tried many combinations of escape characters to no avail. Additionally, I use an identical pattern to extract a value from metadata (using curl, piping, etc) and that works fine. Definitely confused on what is happening here

Best Answer

The easy way to debug this is to add option -v to the sh -c in order to see what systemd is actually passing it. If we do this we can see we are getting (reduced for readability):

curl ... | sed "s/... main-class="hudson...">.../\1/" >>...

The syntax error is that the double-quoted command given to sed has inside it " instead of \". This is because systemd replaces \" by " indiscriminately in the ExecStart string.

You need to pass a backslash to sh by using \\ (which systemd will reduce to \), then the double-quote:

ExecStart=/bin/sh -cv 'curl... | sed "s/...main-class=\\"hudson...

Related Solutions

Systemd – How to Set Environment Variable in Service

Times change and so do best practices.

The current best way to do this is to run systemctl edit myservice, which will create an override file for you or let you edit an existing one.

In normal installations this will create a directory /etc/systemd/system/myservice.service.d, and inside that directory create a file whose name ends in .conf (typically, override.conf), and in this file you can add to or override any part of the unit shipped by the distribution.

For instance, in a file /etc/systemd/system/myservice.service.d/myenv.conf:

[Service]
Environment="SECRET=pGNqduRFkB4K9C2vijOmUDa2kPtUhArN"
Environment="ANOTHER_SECRET=JP8YLOc2bsNlrGuD6LVTq7L36obpjzxd"

Also note that if the directory exists and is empty, your service will be disabled! If you don't intend to put something in the directory, ensure that it does not exist.

For reference, the old way was:

The recommended way to do this is to create a file /etc/sysconfig/myservice which contains your variables, and then load them with EnvironmentFile.

For complete details, see Fedora's documentation on how to write a systemd script.

Systemd: why isn’t it possible to use %i in the first argument of ExecStart=

According to the author himself (poettering) in this thread : it is forbiden because the executable name might be needed in advance (e.g.: SELinux needs this).

But according to other in the same thread and in that one, is still works sometime-ish.

Given that most specifiers can be determined statically in advance (template, machine, etc.) it should get supported eventually.

In the meantime, one solution is to launch a shell, as noted in the question comments and in the first thread:

ExecStart=/bin/sh -c "exec opt/%i/bin/service --args"

Another solution would be to manually invoke the ELF interpreter:

ExecStop=/lib64/ld-linux-x86-64.so.2 /usr/local/bin/%i-cli stop

(Basically the same idea as manually running /usr/bin/perl script.pl instead of trusting the she-bang of the script)

Best Answer

Related Solutions

Systemd – How to Set Environment Variable in Service

Systemd: why isn’t it possible to use %i in the first argument of ExecStart=

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