On 02/18/2015 10:56 AM, Aristeu Rozanski wrote: > Hi Peter, > On Wed, Feb 18, 2015 at 10:40:10AM -0500, Peter Hurley wrote: >> The child is not receiving SIGHUP because /dev/ttyS0 was not set as the >> controlling terminal by ioctl(TIOCSCTTY), which is failing (probably >> with errno == EPERM). You need to check the return value and errno. >> >> To set the controlling tty, the calling process must be a session leader; >> ie., have called setsid() before ioctl(TIOCSCTTY). Check the return value >> for that too. >> >> FWIW, the idiom for starting a session leader is for the parent to >> fork a child and exit and for the child to become the session leader with >> setsid() and establish its controlling tty either with ioctl(TIOCSCTTY) >> or simply opening the first tty. >> >> The reason for this idiom is that setsid() will fail for an existing >> group leader (because otherwise a group leader could abandon existing >> members of its process group, leaving them without a group leader in >> a different session). >> >> I highly recommend Ch 34 of Michael Kerrisk's book, "The Linux Programming >> Interface", especially if this is not a toy project. > > Actually wrote this trying to reproduce a problem a customer is seeing > in a commercial application, but clearly I need to read it. Specifically > about the console behavior, would you recommend the same book?
Ch 34 is about controlling ttys and job control, so it covers the two-tier process hierarchy, foreground and background process groups, and job control signals. Personally, I think the book is invaluable. Unfortunately, consoles are not well documented anywhere. > Every time I need details like this I fail to find any reference online. > Thanks for your help No problem. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
