See below for various troubleshooting hints.
The files shipped by Oracle in the 7.2.x product are incorrect in assuming that you want to setup a parallel server configuration.  The shipped init.ora file has the following line in it:
# define parallel server (multi-instance) parameters
ifile = ora_system:initps.ora
# define parallel server (multi-instance) parameters
#ifile = ora_system:initps.ora
svrmgrl under version 7.3.4.x.
I've had this problem reported to me by a number of people.  Gerald Weber gerald_weber@master.co.at solved it: 
Hi Paul,
first of all thanks for your help,but none of the possible problems you are
thinking about were responsible for my problem.
The problem is the iBCS-emulator itself.
It seems that Oracle performs an sysconf-calls which isn't supported in the
current version of iBCS.
Look at the trace :
<7>[22]615 sysconf(34)
<7>iBCS2 unsupported sysconf call 34
<7>[22]615 sysconf error return linux=-22 -> ibcs=22 <Invalid argument>
<7>[24]615 sysconf(34)
<7>iBCS2 unsupported sysconf call 34
<7>[24]615 sysconf error return linux=-22 -> ibcs=22 <Invalid argument>
Solution:  patching the iBCS-source.apply the following diff-pach :
--- sysconf.c   Sun Apr 19 19:19:15 1998
+++ sysconf.c.ori       Sun Apr 19 19:28:45 1998
@@ -60,7 +60,6 @@
 #define _SC_JOB_CONTROL        5
 #define _SC_SAVED_IDS  6
 #define _SC_VERSION    7
-#define _SC_HACK_FOR_ORACLE 34
 #define _SC_PAGESIZE   11
@@ -97,11 +96,6 @@
                case _SC_SAVED_IDS: {
                        return (1);
                }
-
-               case _SC_HACK_FOR_ORACLE: {
-                 return (1);
-               }
-
                case _SC_PAGESIZE: {
                  return PAGE_SIZE;