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Alan Doherty's Linux tips tricks and gotchas

As I am a Network Consultant I have seen {and made my share} of administrative blunders. I hope to use this section to build up an extensive collection of usefull tips and helpfull information to help others avoid simillar.

This page is obviously not finished, I'm just adding them as i think of them

As obviously a large amount of the paid work i do is correctly and securely configuring linux servers. I cannot offer free support or assistance to users or other consultants experiencing these problem, or attempting to recover from the results. Also the information given here is not neccissarily true for every version of linux and I accept no responsibility for damage caused by someones mis-use of this freely offered advice. If you require help feel free to contact me, but only if you realize you will be charged for this consultancy

most of these have been observed in troubleshooting RedHat linux from 5.2-7.3

Stuff that might not be obvious to the novice, and little stuff even the experienced forget ;)

before you upgrade the current packages {pre up2date} vi rpm -Fvh
1 change to the [empty] destination directory pull down all the rpm's via [ncftp -R ftp://ftp.redhat.com/pub/redhat/linux/updates/{ver}/en/os/*] or [ncftp -R ftp://ftp.esat.net/mirrors/ftp.redhat.com/redhat/linux/updates/{ver}/en/os/i*].
2 Enter the i{4/5/6}86 directory {depends on your processor} take note of the processor specific rpms and purge these rpms from the i386 directory otherwise nastyness may happen.
Now you can fairly safely update/check for dependency issues via rpm -Fvh i{4/5/6}86/*.rpm i386/*.rpm noarch/*.rpm
3 After solving all dependency issues and updating the rpms remember if any kernel rpms have been updated you will have to re-configure and re-run lilo
4 {if kernel not updated stop here} to update lilo [ls /boot/vmlinuz*] take note of the new kernel filename
5 [vi /etc/lilo.conf] change filenames appropriatly
6 [lilo] to apply changes to boot sector
7 {dual boot systems using ntloader only} [dd if=/dev/{linux_boot_device} bs=512 count=1 of=/mnt/{mount_point_of_partition_with_ntloader}/bootsect.lin]
these tips should help you avoid having to use either boot floppy or cdrom-rescue.
step 7 assumes that your dual boot system mounts the partition holding ntloader, if not the file can be written to floppy and manually copied to the ntloader partition
step 7 also assumes that your dual boot systems boot.ini file has a linux entry in the form 'C:\bootsect.lin="Redhat Linux"' if not the filename can be altered in the 'dd' command or you can alter the entry in win.ini
when changing from an older version of sendmail to a recent redhat rpm distributed copy.
be aware that the newer redhat distribution will every startup or restart it will create a new copy of: /etc/aliases.db from /etc/aliases; /etc/mail/virtusertable.db from /etc/mail/virtusertable; /etc/mail/access.db from /etc/mail/access; /etc/mail/domaintable.db from /etc/mail/domaintable /etc/mail/mailertablerun.db from /etc/mail/mailertablerun.
this is because the distributed startup script runs 'newaliases' against /etc/aliases then 'makemap hash' against the other files in /etc/mail/
this can be a problem as some of these source files had alternate locations/names in previous versions and they were manually processed into the database files so if the database source file name and location are not what the startup script expects it will overwrite the manually proccessed database file with a blank database from the new blank files.

Last updated July. 2002 Alan Doherty