Книга: Embedded Linux Primer: A Practical, Real-World Approach

9.2.1. Mounting a File System

9.2.1. Mounting a File System

After a file system has been created, we can mount that file system on a running Linux system, provided that we have access to the hardware device and that the kernel has been compiled with support for our particular file system type, either as a compiled-in module or a dynamically loadable module. The following command mounts the previously created ext2 file system on a mount point that we specify:

# mount /dev/sdb1 /mnt/flash

This example assumes that we have a directory created on our target Linux machine called /mnt/flash. This is called the mount point because we are installing (mounting) the file system rooted at this point in our file system hierarchy. We are mounting the Flash device described earlier that the kernel assigned to the device /dev/sdb1. On a typical Linux desktop (development) machine, we need to have root privileges to execute this command.[70] The mount point is any place on your file system that you decide, which becomes the top level (root) of your newly mounted device. In the previous example, to reference any files on your Flash device, you must prefix the path with /mnt/flash.

The mount command is a powerful command, with many options. Many of the options that mount accepts depend on the target file system type of the mount operation. Most of the time, mount can determine the type of file system on a properly formatted file system known to the kernel. We provide additional usage examples for the mount command as we proceed through this chapter.

Listing 9-3 displays the directory contents of a Flash device configured for an arbitrary embedded system.

Listing 9-3. Flash Device Listing

$ ls -l /mnt/flash
total 24
drwxr-xr-x  2 root root  1024 Jul 18 20:18 bin
drwxr-xr-x  2 root root  1024 Jul 18 20:18 boot
drwxr-xr-x  2 root root  1024 Jul 18 20:18 dev
drwxr-xr-x  2 root root  1024 Jul 18 20:18 etc
drwxr-xr-x  2 root root  1024 Jul 18 20:18 home
drwxr-xr-x  2 root root  1024 Jul 18 20:18 lib
drwx------  2 root root 12288 Jul 17 13:02 lost+found
drwxr-xr-x  2 root root  1024 Jul 18 20:18 proc
drwxr-xr-x  2 root root  1024 Jul 18 20:18 root
drwxr-xr-x  2 root root  1024 Jul 18 20:18 sbin
drwxr-xr-x  2 root root  1024 Jul 18 20:18 tmp
drwxr-xr-x  2 root root  1024 Jul 18 20:18 usr
drwxr-xr-x  2 root root  1024 Jul 18 20:18 var
$

Listing 9-3 is an example of what an embedded systems root file system might look like at the top (root) level. Chapter 6, "System Initialization," provides guidance and examples for how to determine the contents of the root file system.

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