> Unfortuately, it seems that setreuid() doesn't set the real user ID
> as it's supposed to, or at least doesn't do it in a way that makes
> getuid() return the correct value. I can swap the two IDs back if I
> give it the original euid, but I don't get that original euid back from
> getuid():

On most systems the setreuid function does not work in this fashion.
It seems like a gratuitous incompatibility.  I didn't make up my usage
of setreuid; I stole it from kermit.

>     $ cat ts.c
>     /* test reversal of setreuid */
> 
>     #include <sys/types.h>
>     #include <unistd.h>
> 
>     main()
>     {
> 	printf("uid: %d euid: %d\n", getuid(), geteuid());
> 	printf("setreuid = %d\n", setreuid(geteuid(), getuid()));
> 	printf("uid: %d euid: %d\n", getuid(), geteuid());
> 	printf("setreuid = %d\n", setreuid(geteuid(), getuid()));
> 	printf("uid: %d euid: %d\n", getuid(), geteuid());
>     }
>     $ ls -l ts
>     -rwsr-xr-x  1 uucp  staff  13974 Aug 10 18:16 ts
>     $ ./ts
>     uid: 1000 euid: 66
>     setreuid = 0
>     uid: 1000 euid: 1000
>     setreuid = 0
>     uid: 1000 euid: 1000

On my Ultrix (BSD4.2 based) system:

comton> ls -l foo
-rwsrwxr-x   1 uucp     users       50112 Aug 10 22:29 foo*
comton> ./foo
uid: 269 euid: 4
setreuid = 0
uid: 4 euid: 269
setreuid = 0
uid: 269 euid: 4
-- 
Ian Taylor | ian@airs.com | First to identify quote wins free e-mail message:
``[I]n Paris, for example, in 1660 there were 103 holidays in the year.''