Linux Skills

• 1. How to use ramdisk in Ubuntu and Fedora?
• 2. How to enable ssh server in Ubuntu?
• 3. How to disable CPU in Linux?
• 4. How to disable SELinux in Linux?
• 5. How to deal with the errors in MP3 files in Rythmbox under Ubuntu?
• 6. How to accelerate the ssh connection?
• 7. When something goes wrong in ubuntu ?
• 8. How to umount a filesystem even when it is busy?
• 9. How to sync files without copying the originals when using Cloud Storage?
• 10. How to rename multiple files at a time?
• 11. What is the most amazing ssh option you have encountered?
• 12. When Ubuntu Xsession goes wrong….

In Fedora, the ramdisk is disabled by default, that is, it is compiled into the kernel, but as a module, which will be loaded into the kernel when actually used. So, it is necessary to compile the kernel manually to select the ramdisk as the built-in modules.

In Ubuntu, the ramdisk support is enabled by default, so the steps are easier compared to Fedora.

Using the following commands to list the ramdisk:

The output will be like:

Format the ramdisk as an ext4fs:

Then mount it:

By default, Ubuntu doesn‘t install the ssh server, so the following command will fail:

Using the following command to install the ssh-server:

Then all things will go well.

It is easy to do with real root user:

The CPU status can be checked by:

To re-enable the CPU:

The SELinux has some negative effect on the self-defined filesystem, so it is necessary to disable it, using the following command:

will list the status of the SELinux,

To change the status of SELinux, modify the configure file in:

The easiest way is as follows:

Add the following two lines to the end of the file:

This enables the Chinese characters to be recoginized by the system.

I am working on a project which has something to do with a remote server, and I have to ssh to that server, but the server is Fedora and my os is Ubuntu, and it turns out it takes a long time to resove the host/server IP, the solution to this problem is:

Afer a failed attempt to upgrade the Ubuntu13.10 to Ubuntu 14.04, the system shows a popup window everytime the system boots, the title of the window is "System Program Problem Detected". The following method can be used to solve the problem:

This command will delete the crushed software of the system so that the reporting utility won‘t work, thus eliminating the annoying message.

Recently, a project requires frequently mounting and testing a filesystem, and it is very likely that the newly-mounted filesystem will crash for all kinds of reasons, and after the accident, it is no longer possible to umount the filesystem in a normal way. The error message from the OS is as follows:

With the -l option of umount, the result can be seen as follows:

When using CloudDrive, it is likely that the software may only allow you to synchronize the files or folders under a specific folder, if you have many other directories to synchronize, you have to copy files, but there is a simple way to achieve the same goal without copying files—the symbolic link.
In Linux,the following command can be used to create a symbolic link to another directory:

\\

In windows, use the following command:

1. Add extention to all the files in a directory: \

   for f in *;do mv "$f" "$f.png";done

2. Rename: \

   rename ‘s/old-name/new-name/‘ files

The first useful option of ssh is the GSSAPIAuthentication=no, which accelerates the connection startup time. Another useful option is the X11 forwarding, with the -X option, you can use the X11 application from the localhost.(Especially for emacs).

The problem I encountered is like this:
When I want to logout the xsession of ubuntu, it fails to close all the running application and return back to the login screen, so I start a terminal by ALT+CRTL+F1, from which I did a reboot. After the system booted, I typed my password to my account, but it returned back to the login session again, and the process continued.

There was some error messages in ~/.xsession-error file, and the mode bits of ~/.xauthority file has changed to root only, so the correct way to deal with the problem is use the following command: