signals and RFC4254

Howard Chu hyc at
Thu Jun 17 19:34:55 EST 2010

This may be more relevant to an IETF mailing list but I figured I'd start here 
first. I ran across this because signals need to be sent as explicit commands, 
not as special characters, when using EXTPROC. So I started implementing the 
"signal" channel request. However, the description of the request is inadequate.

RFC4254 section 6.9 says the 'signal name' values are the same as discussed in 
6.10 for the "exit-signal" message. But that list of signals is specifically 
limited to values that can cause a program to exit, and be returned in a 
program's exit status. This list of signals you can *receive* on exit is only 
a subset of the signals you might want to *send* with a "signal" channel 
request. In particular, if you want to support sending all of the signals that 
can be generated by keyboard input, the suspend character is missing (SIGTSTP).

I guess we can live without most of the others, but possibly SIGCONT and 
SIGSTOP might be useful too. I think TSTP should be part of the base spec, 
(and not an xx at extension) otherwise this channel request can't fulfill 
the most basic need (propagating signals from a terminal to an app).
   -- Howard Chu
   CTO, Symas Corp. 
   Director, Highland Sun
   Chief Architect, OpenLDAP

More information about the openssh-unix-dev mailing list