The message means that the app your
.service file started with
ExecStart= exited and set the return code to 10 when it did so.
There is no single uniform standard (although there are several partial standards and conventions) on result codes, so the only way to find out what the code 10 means is reading the documentation of that specific app... or its source code, if the documentation does not specify it.
So systemd does not know what code 10 means, so it adds n/a to indicate that no verbal description is available from systemd. You've not told us what the app in question is, so we cannot look up result code 10 for you any further than this.
In the documentation of
systemd, there are several tables of result code conventions. To summarize:
- the C library basically defines just 0 for OK and 1 (or any non-zero value) for failure
- the Linux Standards Base (LSB) has definitions for codes 2...7, for things designed to be used as services (or originally for SysVinit-style service startup scripts)
the LSB specification suggests that codes 200 and above would be implementation-specific, and so
systemd defines a set of codes in that range for errors generated by
the BSD operating systems define a group of generically useable exit codes in range 64..78. The definition for these codes is typically available on Linux systems too, in file
/usr/include/sysexits.h, if the C development packages have been installed on the system.
But none of these are saying anything about code 10, so no guesses can be made without knowing the application in question.