Hi,
first of all check the contents of logs in $SDEHOME/etc (for example, sde_esri_sde.log)
double check with with the contents of the following files (services.sde,dbinit.sde)
double check your environment variables and check that you can execute "sqlplus" within your shell as "sde" Linux User.
if you can't sqlplus then its a 'sticky bit' issue:
cd $ORACLE_HOME/bin
ls -l oracle
chmod 6751 oracle
* concerning your remakr about "giomgr.defs " file, the file should exist under $SDEHOME/etc. if not, you need to re-install the ArcSDE 10.1 binary again.
* from personal experience: when i upgrade from major version to another (i take backup of the following files : giomgr.defs,dbtune.sde) just in case.
update us please if you have resolved it and share the soultion.
Thanks,
Emad Al-Mousa