#########################

term% file ./pstotext
.../pstotext: 386 plan 9 executable

term% grep denied *.[ch]

term% grep 'Permission denied' *

[the following is piggy, but worked :-) ... ]
pstotext: [snip] ... blah blah blah ...Directory not emptyNottyNxioPermission deniedBroken pipeRead-only file system ... blah blah blah ...[snip]

[...thus pointing me at sys libs]
term% rgrep 'Permission denied' '*.c' /sys/src/ape
/sys/src/ape/cmd/pdksh/missing.c:		return "Permission denied";
/sys/src/ape/lib/ap/stdio/strerror.c:	"Permission denied",

term% rgrep 'Permission denied' '*.h' /sys/src/ape

term%
[rgrep is "recursive grep" script]

term% rgrep   'EPERM' '*.h' /sys/include
/sys/include/ape/errno.h:#define EPERM	30

term%
[thus, it is probably #define EPERM	30 from /sys/include/ape/errno.h    ... however, errno.h is included so many times from allmost everywhere, that I am (hopefully temporarily) lost :-(((   ... I'm digging. ]

#########################
 C gurus: Any hints, please?  A more comprehensive description of errno 30 than "Permission denied" is welcome...
#########################

TIA,
cheers,
++pac.