One line to remove all unneeded old kernel for Ubuntu

     Along with the kernel keeps updating, many old kernels are kept in the system. For normal users, those old kernels are no longer needed, so the best way just remove them.
     To remove all kernels, just run the single line with below:

*Original post from here

Ubuntu Desktop Screen Upside down??

     I used to have an Nvidia video card on Ubuntu and use Nvidia Xserver drive for it, but couple days ago I decided to remove that card and use the onboard video card which is INTEL GMA 950.
     After take the Nvidia out, I have to generate the new xorg.conf file for the X Windows and new video device. So, just use Ctrl + Alt + F1 switch to text mode, and run:

     After reboot, the desktop screen become to upside down. Even can’t type anything in terminal. To fix it, just switch to text mode again, rename “/etc/X11/xorg.conf” to “/etc/X11/xorg.conf.new”, then reboot. The screen is back to normal but no video driver, then use synaptic to find any package beginning with “nvidia”, and remove them all. Last thing is change “/etc/X11/xorg.conf.new” back to “/etc/X11/xorg.conf” and reboot, then all set.

Create tablespace on NFS based LINUX + Oracle

     When the first time to create tablespace on SQLplus, it shows:

“ORA-27040: file create error, unable to create file. Linux-x86_64 Error: 13: Permission denied”

So I just change my home directory to “777”, then getting the error

“ORA-27054: NFS file system where the file is created or resides is not mounted with correct options”

     After check the “autofs” settings, I found the content of file “auto.home” has problem which is something wrong with NFS mount options. The solutions is change the original content

* -fstype=nfs,soft,intr,rsize=8192,wsize=8192,nosuid,tcp oracle.server.com:/users/&

to

* -rw,bg,hard,intr,rsize=32768,wsize=32768,suid,nfsver=3,tcp oracle.server.com:/users/&

SSH + X11 display after su to another user

     Sometimes we need to run the X11 application window via SSH. For example, I am user “A”, and SSH to host “example”. To be possible running X11 application window, we need to type the command:

#ssh -Y A@example

     In addition to the SSH restriction, we need to run an X application as someone other than yourself. For example, the Virtualbox can be only run by user “B”. If the user “A” can sudo to become user “B” or “A” is the root, in order to allow user “B” access to user “A”’s display, B needs to import “A”’s .Xauthority cookie. We can use xauth to accomplish this and it’s a quick one-liner before sudo su - B:

     A@example:~#xauth extract – :`echo $DISPLAY |awk -F: ‘{print $2}’` | sudo su – B -c “/usr/bin/xauth merge -”
     A@example:~#sudo su – B
     B@example:~#VirtualBox &

VI中替换命令的具体用法

      VI中替换命令可以简单的写成以下命令：

:[range]s /[st1]/[st2]/g

其中:

• [range]表示替换命令的查找范围：
  • 1. “%” 表示所有行
  • 2. “.” 表示当前行
  • 3. “$” 表示最末行

       例如，:%s/[st1]/[st2]   表示查找文件中所有[st1]的字符串，并替换成[st2]
                :-5，+5s/[st1]/[st2]   表示查找目前行的前五行和后五行中[st1]的字符串，并替换成[st2]

• “s”表示替换命令
• [st1]表示要查找的字符串
• [st2]表示希望把匹配的字符串变成的字符串
• “g”表示可选项，放在命令末尾,表示对搜索字符串的每次出现进行替换;不加 g,表示只对搜索字符串的首次出现进行替换;g 放在命令开头,表示对正文中所有包含搜索字符串的行进行替换操作。