[oracle@ora10g database]$ ./runInstaller
Starting Oracle Universal Installer...
Checking installer requirements...
Passed
All installer requirements met.
Preparing to launch Oracle UniversalInstaller from /tmp/OraInstall2012-09-16_01-54-05AM. Please wait ...
Error in writing to directory/tmp/OraInstall2012-09-16_01-54-05AM. Please ensure that this directory iswritable and has atleast 60 MB of disk space. Installation cannot continue.
: Success
提示是/tmp 空间不够，不过我这里不是这个原因，后来检查了一下环境变量。也没有问题。
最终还是安装文件的权限问题导致：
[oracle@ora10g database]$ ll
total 67
drwxr-xr-x 1 root root 4096 Oct 20 2005 doc
drwxr-xr-x 1 root root 4096 Oct 23 2005 install
drwxr-xr-x 1 root root 4096 Oct 23 2005 response
-rwxr-xr-x 1 root root 1326 Oct 23 2005 runInstaller
drwxr-xr-x 1 root root 49152 Oct 23 2005 stage
-rwxr-xr-x 1 root root 5416 Oct 20 2005 welcome.html
修改成：
[oracle@ora10g software]$ ll
total 36
drwxr-xr-x 9 oracle oinstall 4096 Sep 1602:07 doc
drwxr-xr-x 5 oracle oinstall 4096 Sep 16 02:07 install
drwxr-xr-x 2 oracle oinstall 4096 Sep 16 02:07 response
-rwxr-xr-x 1 oracle oinstall 1326 Sep 16 02:07 runInstaller
drwxr-xr-x 9 oracle oinstall 12288 Sep 1602:09 stage
-rwxr-xr-x 1 oracle oinstall 5416 Sep 16 02:09 welcome.html
安装文件改成Oracle用户后，成功安装。
根据MOS的说明，导致这个错误可能有如下原因：
a) Insufficient free space in the temporarydirectory.
b) Insufficient access rights on the temporary directory.
c) On Oracle 9.2.0.5 to 9.2.0.8, a bug like bug: 5614628.
d) Not using a (local) console.
e) Corrupted software set.
f) Setup of the Oracle software in the stage area on disk.
g) Wrong Unzip utility is used.
h) No execute permission on Unzip utility
i)Free space => 2Tb
j)During ftp from a Windows mounted DVD to an Unix system (unzipped directories),the new directories in the stage area on Unix are all in lowercase.
参考：
Oui Fails With 'Error InWriting To Directory /Tmp/Orainstall...' [ID 407095.1]