OK, I went a bit deeper into this now...
I have retried the whole installation procedure on a new clean VM.
I've installed IBM Java 1.4.2, and now sapinst created all the users, not me.
Now, when the first assertion failed error comes up, the xuser list command is empty.
I have used these commands to create users:
su -c "/opt/sdb/programs/bin/xuser -U DEFAULT -u n04adm,sapn04adm -d N04 -n N04 -S SAPR3 -t 0 -I 0 set" -l n04adm
su -c "/opt/sdb/programs/bin/xuser -U c -u control,sapn04adm -d N04 -n N04 -S SAPR3 -t 0 -I 0 set" -l n04adm
su -c "/opt/sdb/programs/bin/xuser -U c_J2EE -u control,sapn04adm -d N04 -n N04 -S SAPR3 -t 0 -I 0 set" -l n04adm
su -c "/opt/sdb/programs/bin/xuser -U w -u superdba,sapn04adm -d N04 -n N04 -S SAPR3 -t 0 -I 0 set" -l n04adm
What I realized now, is, that sapn04adm stands for the password, and I have entered a different one in sapinst. Therefore, I have re-executed the 4 commands, using the password which I supplied to sapinst. Unfortunately, still couldn't connect to the DB.
Then I've tried to re-execute with clear and then set, but still no luck.
Then I've realized, that the password can't be longer than 8 characters, hence I tried sapn04ad.
And again no luck. Now I'm wondering what to do... Why sapinst isn't creating those users by itself...
And what to do... ? Perhaps if I reinstall everything again and supply to both sapinst and to the xuser creation command the same passwords, it might work... ?
PLEASE help me, I'm going nuts about this !!