问题：

SQL> conn / as sysdba
ERROR:
ORA-09817: Write to audit file failed.
Linux-x86_64 Error: 28: No space left on device
Additional information: 12
ORA-01075: you are currently logged on
分析原因：（经百度查询造成的原因是audit所在的文件系统满了，没有多余的空间）

查看报错日志：cd /u01/app/oracle/diag/rdbms/ora11gr2/ORA11GR2/trace   tail -100f alert_ORA11GR2

Non critical error ORA-48113 caught while writing to trace file "/u01/app/oracle/diag/rdbms/ora11gr2/ORA11GR2/trace/ORA11GR2_mmon_21952.trc"

Error message:

Writing to the above trace file is disabled for now

查看磁盘占用情况：

[oracle@oracle trace]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3              22G   21G     0 100% /
/dev/sda1              99M   22M   73M  23% /boot
tmpfs                1002M  371M  631M  38% /dev/shm
/dev/sr0              3.6G  3.6G     0 100% /media/Oracle Linux Server dvd 20110119
/dev/sr0              3.6G  3.6G     0 100% /mnt
到trace目录下删除日志：

[root@oracle trace]# rm -rf *.trm

[root@oracle trace]# ls

alert_ORA11GR2.log

删除日志之后可以正常连接。