Understanding the Linux /boot directory

When I first began using Linux quite some time ago, I remember thinking to myself WTF is all this stuff in /boot. There were files related to grub, a file called vmlinuz, and several ASCII text files with cool sounding names. After reading through the Linux kernel HOWTO, the /boot directory layout all came together, and understanding the purpose of each file has helped me better understand how things work, and allowed me to solve numerous issues in a more expedient manner. Given a typical CentOS or Fedora host, you will probably see something similar to the following in /boot:

$ cd /boot

$ tree

|-- System.map-
|-- System.map-2.6.30
|-- config-
|-- config-2.6.30
|-- efi
| `-- EFI
| `-- redhat
| `-- grub.efi
|-- grub
| |-- device.map
| |-- e2fs_stage1_5
| |-- fat_stage1_5
| |-- ffs_stage1_5
| |-- grub.conf
| |-- iso9660_stage1_5
| |-- jfs_stage1_5
| |-- menu.lst -> ./grub.conf
| |-- minix_stage1_5
| |-- reiserfs_stage1_5
| |-- splash.xpm.gz
| |-- stage1
| |-- stage2
| |-- ufs2_stage1_5
| |-- vstafs_stage1_5
| `-- xfs_stage1_5
|-- initrd-
|-- initrd-2.6.30.img
|-- vmlinuz-
`-- vmlinuz-2.6.30

For each kernel release, you will typically see a vmlinuz, System.map, initrd and config file. The vmlinuz file contain the actual Linux kernel, which is loaded and executed by grub. The System.map file contains a list of kernel symbols and the addresses these symbols are located at. The initrd file is the initial ramdisk used to preload modules, and contains the drivers and supporting infrastructure (keyboard mappings, etc.) needed to manage your keyboard, serial devices and block storage early on in the boot process. The config file contains a list of kernel configuration options, which is useful for understanding which features were compiled into the kernel, and which features were built as modules. I am going to type up a separate post with my notes on grub, especially those related to solving boot related issues.

This article was posted by Matty on 2009-07-02 03:55:00 -0400 -0400