Connection with SQL*Plus to Oracle I've installed Oracle Database Express 10g on Ubuntu, but the following error occures when I try to connect to sql plus using the sysdba as username and it's password which I gave during installation :

ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux Error: 2: No such file or directory
Process ID: 0
Session ID: 0 Serial number: 0


These are some iformations I think they may help :

uname -a

Linux aimad-Vostro-1015 3.11.0-17-generic #31-Ubuntu SMP Mon Feb 3 21:53:31 UTC 2014 i686 i686 i686 GNU/Linux


env | grep ORACLE

ORACLE_SID=XE
ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server


sysctl -p |grep kernel

kernel.shmall = 2097152
kernel.shmmni = 4096
kernel.sem = 250 32000 100 128
kernel.shmmax = 1073741824


sysctl -a |grep kernel | grep shm

kernel.shm_next_id = -1
kernel.shm_rmid_forced = 0
kernel.shmall = 2097152
kernel.shmmax = 1073741824
kernel.shmmni = 4096


sysctl -a | grep kernel | grep sem

kernel.sem = 250    32000   100 128
kernel.sem_next_id = -1


df -k /dev/shm

Filesystem     1K-blocks  Used Available Use% Mounted on
none             1014392   156   1014236   1% /run/shm


How can I solve this problem ?
You must install Oracle as a non-root user.  Generally, that user would be called oracle, but it can be anything, as long as it's not root.