Re: [PLUG] Linux n00b question

[JP Vossen <jp@jpsdomain.org>]

> Date: Sun, 9 Jan 2011 14:09:59 -0500
> From: "K.S. Bhaskar"<bhaskar@bhaskars.com>
> Subject: Re: [PLUG] Linux n00b question

> I always set up a system with two alternate root partitions.

Yeah, I usually do that using RAID1, but on a laptop with 1 drive this 
is better (since it'll actually work).  John K just suggested that too. 
 Nice.

[...]
> I always set up an encrypted /home.? But I configure my PC so that I
> can login without /home mounted. When I cross an international border
> with my laptop, I always cross it with the laptop powered down. Then
> if I am asked to boot it, I boot it, and can login - but it will be an
> innocuous /home, not my real /home (not that I have ever been asked to
> boot my laptop - just a sensible precaution, IMHO). To mount the
> encrypted /home, I login as root and run a shell script:

Neat idea.  I have to think about that.  If you do not have /home/ as a 
separate partition, you could also just do a loopback mount of some 
other (encrypted) FS on top of /home/...  Hummm...


> #!/bin/bash
> #
> # Get password and mount /home
> #
> umount /home>&/tmp/umounthome_$$_`date +%Y%m%d%H%M%S`.log
> cryptsetup remove sda2-aes>&/tmp/cryptsetupremove_$$_`date +%Y%m%d%H%M%S`.log
> cryptsetup -c aes -s 256 create sda2-aes /dev/sda2
> 2>/tmp/cryptsetup_$$_`date +%Y%m%d%H%M%S`.log
> fsck -a -t jfs /dev/mapper/sda2-aes | tee /tmp/fsck_$$_`date +%Y%m%d%H%M%S`.log
> mount -o relatime /dev/mapper/sda2-aes /home>&/tmp/mount_$$_`date
> +%Y%m%d%H%M%S`.log
> swapon /home/swap

Oh, you're killing me!!!  Personal pet peeve: running external programs 
(like date) during every line of your script unnecessarily.  Yes, for 
this script it doesn't matter; it's still a bad habit.  :-)

More efficient (alignment is more personal preference):

LOG_FILE="/tmp/umounthome_$$_`date +%Y%m%d%H%M%S`.log"
FSCK_LOG_FILE="/tmp/fsck_$$_`date +%Y%m%d%H%M%S`.log"
umount /home                                       >& $LOG_FILE
cryptsetup remove sda2-aes                         >& $LOG_FILE
cryptsetup -c aes -s 256 create sda2-aes /dev/sda2 2> $LOG_FILE
fsck -a -t jfs /dev/mapper/sda2-aes             | tee $FSCK_LOG_FILE
mount -o relatime /dev/mapper/sda2-aes /home       >& $LOG_FILE
swapon /home/swap


FYI, bash 4.2 will introduce new printf arguments to just "printf" the 
date.  It's always bugged me that the shell knows what time it is (e.g. 
the prompt \D argument) but you need to use an external program to 
display it in a script.  As of bash 4.2 you don't anymore.  I suggested 
that to Chet a while ago, but to be fair other shells have also 
implemented it (*cough* Paul, zsh, I think *cough* :), so I'm not sure 
what prompted him to add it to bash.

Later,
JP
----------------------------|:::======|-------------------------------
JP Vossen, CISSP            |:::======|      http://bashcookbook.com/
My Account, My Opinions     |=========|      http://www.jpsdomain.org/
----------------------------|=========|-------------------------------
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