Troubleshooting in Linux
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* Boot Related
* File System Related
* User Related
5 1/2 Hours
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TS Session A - 2 1/2h Session B 3h
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10 questions 20-25 questions
5 cumpulsary 1h RHCT min70% RHCE min70%
5 choice 1 1/2 Installation sendmail
F.S+RAID+LVM postfix
rpm,nic,xwindows squid
cups,crontab samba
user administration ftp,nfs,nisclient
Troubleshooting - Boot Related
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steps to look
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1. bios
2. grub
grub-install /dev/hda <--- in rescue mode
3. /etc/grub.conf <--- if any line is missing - add the line
<--- if grub.conf file is missing - cmd line booting
4. /boot/
vmlinuz |
initrd | <--- if these files are missing
If vmlinuz is missing
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* mount the nfs share
* cp the kernel-2.6.9-42.EL...rpm to /misc
* cp /misc
* rpm2cpio kernel....rpm > llc
* cpio -ivd <>
* cp vmlinuz-2...EL to the /boot directory
If initrd is missing
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or
* mkinitrd /boot/initrd-`uname -r`.img
5. if /sbin/init is missing <--- reinstall SysVinit
6. contineous reboot/shutdown <--- in /etc/inittab
goto single user mode & change the values in /etc/inittab
7. /etc/fstab
To clear the bootloader from mbr
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# dd if=/dev/zero of=/dev/hda bs=446 count=1
To install grub bootloader in mbr
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boot: linux rescue
-/bin/sh-3.00# chroot /mnt/sysimage
sh-3.00# grub-install /dev/hda
sh-3.00# reboot
If kernel panic comes steps to do
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grub> root
grub> kernel /vmlinuz-2.6.9-42.EL.img ro root=LABEL=/
grub> initrd /initrd-2.6.9-42.EL.img
grub> boot
If fstab file entry is changed steps to do
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1 # mout -o remount,rw /
2 # /bin/vi /etc/fstab
Troubleshooting - User Related
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* Password forgot <--- single user mode
* Login failed <--- goto /etc/password in last field /sbin/nologin
* /etc/inittab <--- tty - terminals commented
* /etc/shadow <--- password age set
* (none) login <--- /bin/bash is renamed with some other. single user mode
cd /mnt/sysimage
cd bin
mv bash.xxx bash