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The Linux Kernel HOWTO: Tips and tricks Next Previous Contents

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 (nelson@crynwr.com) 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 ftp.emlist.com in pub/kchanges or through the URL


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