September 24, 2008

Vi/Ex script line mode

Filed under: Ex, linux, Vi — Tags: , , — lancevermilion @ 5:09 pm

This would edit “/etc/” which is owned by root and allow you to add “/usr/local/BerkeleyDB.4.6/lib” to the end of the file. “$” represents the last line of the file (this is determined by Vi/Ex). If you were to put the number “5” in place of “$” and there was only 2 lines in the file this would fail since that line does not exist.

sudo ex - /etc/ << BLAH
$ append

This will search “/etc/openldap/slapd.conf” for “var//” and replace that with “var/” AND “etc//” and replace that with “etc/”.

sudo ex - /etc/openldap/slapd.conf << BLAH

Reference Here for a command guide.
Reference Here for a tutorial.


September 15, 2008

Password recovery Linux CentOS/RedHat

Filed under: linux — lancevermilion @ 12:52 pm

First, try single user. If you don’t see either a LILO or GRUB boot screen, try hitting CTRL-X to get one. If it’s LILO, just type “linux single” and that should do it (assuming that “linux” is the lilo label). If GRUB, hit ‘e”, then select the “kernel” line, hit “e” again, and add ” single” (or just ” 1″) to the end of the line. Press ENTER, and then “b” to boot.

You should get a fairly normal looking boot sequence except that it terminates a little early at a bash prompt. If you get a “Give root password for system maintenance”, this isn’t going to work, so see the “init” version below.

If you do get the prompt, the / filesystem may not be mounted rw (although “mount” may say it is). Do

mount -o remount,rw /

If that doesn’t work (it might not), just type “mount” to find out where “/” is mounted. Let’s say it is on /dev/sda2. You’d then type:

mount -o remount,rw /dev/sda2

If you can do this, just type “passwd” once you are in and change it to whatever you like. Or just edit /etc/shadow to remove the password field: move to just beyond the first “:” and remove everything up to the next “:”. With vi, that would be “/:” to move to the first “:”, space bar once, then “d/:” and ENTER. You’ll get a warning about changing a read-only file; that’s normal. Before you do this, /etc/shadow might look like:


and after, the first few lines should be:


You’ll need to force the write: with vi, “:wq!”. (If that still doesn’t work, you needed to do the -o remount,rw, see above).

Another trick is to add “init=/bin/bash” (LILO “linux init=/bin/bash” or add it to the Grub “kernel” line). This will dump you to a bash prompt much earlier than single user mode, and a lot less has been initialized, mounted, etc. You’ll definitely need the “-o remount,rw” here. Also note that other filesystems aren’t mounted at all, so you may need to mount them manually if you need them. Look in /etc/fstab for the device names.

Keep this in mind if you have a Linux machine in a publically accessible place : without more protection, it’s not usually hard to recover a lost root password, which means it’s just as easy for someone to CHANGE it, or access root without your knowlege.

Another way to do this is to remove the password from /etc/shadow. Just in case you screw up, I’d copy it somewhere safe first. You want to end up with the root line looking something like this:

# original line

# after editing

If you are having trouble with editing (you really do have to learn vi one of these days), you could just (after making a copy, of course) just

echo "root::12832:0:::::" > /mnt/etc/shadow
or, if you were in single user mode
echo "root::12832:0:::::" > /etc/shadow

and then fix things up when rebooted.

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