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11. Tips and tricks

11.1 Redirecting output of the make or patch commands

If you would like logs of what those `make' or `patch' commands did, you can redirect output to a file. First, find out what shell you're running: `grep root /etc/passwd' and look for something like `/bin/csh'.

If you use sh or bash,

    (command) 2>&1 | tee (output file)
will place a copy of (command)'s output in the file `(output file)'.

For csh or tcsh, use

    (command) |& tee (output file)

For rc (Note: you probably do not use rc) it's

    (command) >[2=1] | tee (output file)

11.2 Conditional kernel install

Other than using floppy disks, there are several methods of testing out a new kernel without touching the old one. Unlike many other Unix flavors, LILO has the ability to boot a kernel from anywhere on the disk (if you have a large (500 MB or above) disk, please read over the LILO documentation on how this may cause problems). So, if you add something similar to

    image = /usr/src/linux/arch/i386/boot/bzImage
        label = new_kernel
to the end of your LILO configuration file, you can choose to run a newly compiled kernel without touching your old /vmlinuz (after running lilo, of course). The easiest way to tell LILO to boot a new kernel is to press the shift key at bootup time (when it says LILO on the screen, and nothing else), which gives you a prompt. At this point, you can enter `new_kernel' to boot the new kernel.

If you wish to keep several different kernel source trees on your system at the same time (this can take up a lot of disk space; be careful), the most common way is to name them /usr/src/linux-x.y.z, where x.y.z is the kernel version. You can then ``select'' a source tree with a symbolic link; for example, `ln -sf linux-1.2.2 /usr/src/linux' would make the 1.2.2 tree current. Before creating a symbolic link like this, make certain that the last argument to ln is not a real directory (old symbolic links are fine); the result will not be what you expect.

11.3 Kernel updates

Russell Nelson ( summarizes the changes in new kernel releases. These are short, and you might like to look at them before an upgrade. They are available with anonymous ftp from in pub/kchanges or through the URL

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