Runtime Errors Boot Loader Problems and Kernel Oops

Runtime errors occur as the kernel is loading. Error messages are displayed on the screen or written to the var log messages file. Bootloader problems display messages to the screen no log file is produced. Kernel oops are errors in a running kernel, and error messages are written to the Excellent documentation on the Internet exists for troubleshooting just about every type of error that LILO, GRUB, or the kernel could give during boot. The best way to find this documentation is to go to your...

Beginning the Boot Loading Process

Although the actual boot loading mechanism for Linux varies on different hardware platforms (such as the SPARC, Alpha, or PowerPC systems), Intel-based PCs running Ubuntu most often use the same mechanism throughout product lines. This process is accomplished through a Basic Input Output System, or BIOS. The BIOS is an application stored in a chip on the motherboard that initializes the hardware on the motherboard (and often the hardware that's attached to the motherboard). The BIOS gets the...

Index

SYMBOL A B C D E F G H I J K L M N O P Q R S T U V W X Z PAM (Pluggable Authentication Modules) parted command, Ubuntu installation partitions Ubuntu installation 2nd 3rd passive command passwd command 2nd passwd files passwords etc passwd fil batches, changing in bootloaders brute-forcing FTP users GRUB LDAP root users, assigning to MySQL root users PostgreSQL database users, creating remote computer logins security shadow 2nd system password policies Ubunbtu installation usernames patch...

The badblocks Command

Although not a performance tuning program per se, the utility badblocks checks an (preferably) unmounted partition for bad blocks. It is not recommended that you run this command by itself, but rather allow it to be called by fsck. It should only be used directly if you specify the block size accuratelydon't guess or assume anything. The options available for badblocks are detailed in the man page. They allow for very low-level manipulation of the file system that is useful for data recovery by...

Reformatting with the s Option When Experiencing Unrecoverable File System Errors

In attempting to recover data from a damaged disk with file system errors that cannot be fixed with fsck, you can run the mke2fs command with the -s option like this (for example, if you are having trouble with the ext2 3 partition on dev hda2) The -s argument writes new superblock information, but does not write new inodes this might make the missing data salvageable, or it might not depending on the damage. You must run e2fsck on the unmounted partition after using the mke2fs command in this...

Undeleting Files Using mc

The Midnight Commander can make use of a virtual file system and includes a special undelete file system that can be used on ext2 3 partitions. The mc utility is just an interface to the ext2fs library, and the virtual file system handles for you the nitty-gritty details of the file system that the previous paragraph alluded to. As with any simplified solution to complex issues, mc must make some assumptions for you that might result in less data being recovered than if you use the manual...

Capturing Screen Images

You can use graphics manipulation tools to capture images that are displayed on your computer screen. Although this technique was used for the production of this book, it has broader uses there is truth to the clich, that a picture is worth a thousand words. Sometimes it is easier to show an example than it is to describe it. A captured screen image (also called a screen grab or a screenshot) can be used to illustrate an error in the display of an application (a font problem, for example) or an...

Fun with Image Magicks identify

You can use ImageMagick's identify command to identify details about image files. The welcoming splash image used for the GRUB bootloader is located in boot grub and is a gzipped .xpm image. If you run identify on the image, you'll discover that it's a 640x480 xpm image with 16-bit color depth. That's all you need to know to construct a replacement image of your own. Using the GIMP or another graphics tool, crop or resize your chosen image to 640x480 and change the color depth to 16 bits. Save...