Moving var to hard disk on embedded Linux....

shylock_1 · 03-02-2010, 06:54 PM

Hi Forum,

Is any body know how to move var which is on the 8MB ROM to Hard disk????

I have following scenario:

1/ On IBM powerPC with 8MB ROM and 64MB RAM
2/ Entire Linux 2.6.9 OS with application the image size is 5.1MB
3/ The image get flashed in to ROM and creates var directory on ROM area
4/ Recent upgrade with Hard drive for 60GB gave more storage power
5/ Hence, moving var on to hard disk IS first priority, so var store larger size of data and log, following is snapshot of content on ROM

Code:

bin       etc       lib       proc      sbin      sys       var
dev       hdd       mnt       root      share     tmp       var_init

My goal is ....

1/ Move var to hard disk with all its contents
2/ the IDE hard disk recognised by OS as hdd and mounted in ROM as directory
3/ Once var is moved on the hard disk then OS should look for all setting and data, log etc on hard drive based var directory hence kernel must look for all necessary files on hdd/var directory
4/ The original var could be remain on ROM but made empty and not to be used by OS.
5/ The entire OS on ROM area is READ only and cannot be deleted i.e. var directory hence only var contents moved to hdd/var directory.
6/ The file /etc/fstab is completely blank with zero size.

I appreciate some body knows how to move var from readonly (squashfs) file system to hard disk.
Thanks in advance.

jlinkels · 03-02-2010, 07:54 PM

Create a partition on you hard disk to hold /var. Format it with your favorite file system. Let's say this partition is /dev/sdb3.

With your squashed installation started up & running, copy the contents of you current var into an aribtrary place. Issue this command:

Code:

mount /dev/sdb3 /var

Copy the copied contents of the original /var to the new /var.

To do this mounting automatically you'd need to change the fstab and resquash the file system. The line in the fstabe must become:

Code:

/dev/sdb3 /var   ext3  defaults   0   2

Check the file system type.

However, these ROM installations often have an unsquashed part on the ROM device where you can easily add additional configuration. Being this either your own fstab, or a script which does the mount for you.

jlinkels

shylock_1 · 03-03-2010, 08:17 AM

Thanks jlinkels

Currently the hard drive already mounted on OS as a hdd directory if I issue:

Code:

~ > ls
bin       etc       lib       proc      sbin      sys       var
dev       hdd       mnt       root      share     tmp       var_init

~ > cd hdd
/mnt/hdd1 > ls
download      log           movie         pictures      swapswapfile
epg           lost+found    photos        swapfile      tmp
/mnt/hdd1 >

The above is snapshot from device /mnt/hdd1 mounted in mnt directory. If I check cd hdd I can view all the contents of hdd and subsequently create directory and copy contents of var but making kernel to read from the /mnt.hdd1/var is tricky cause currently fstab file is completely blank and READ ONLY. When I try to edit using vi the message pops up readonly cannot write.

CAUSE file system squashFS applies on /etc/ file system too.

the question is how to make /etc/fstab? Although I tried to

Code:

/etc > chmod +x fstab
chmod: fstab: Read-only file system

jlinkels · 03-03-2010, 08:54 AM

Squashfs is a compressed file system, which is uncompressed at the time of booting. It can safely be mounted as RO because it is not to be expected that someone has to make changes.

In order to access fstab in a squashfs file system, you'd have to UNsquash the squash file, make you changes and squash it back again.

jlinkels

shylock_1 · 03-03-2010, 10:13 AM

Right... if Understood correctly? I am using telnet to communicate STBox running Linux Kernel 2.6.9

Preliminaries...
1/ The Hard disk is already formated and MOUNTED as /mnt/hdd1 with smylink as hdd at the / directory
2/ Therefore, no need to format or mount hard disk?

Secondary

3/ Copy the contents of /var directory to else where ... say /hdd/tmp/var (/mnt/hdd1/tmp/var)
4/ Once the content of var copied else where then issue command

Code:

mount /dev/hdd1 /var

5/ Above command will mount the var on hdd (/mnt/hdd1/var) for only current SESSION?
6/ Once mounted var restore all its contents from (/mnt/hdd1/tmp/var) to hdd/var (mnt/hdd1/var)

Hay presto... this will work for current session?

Automatic mount of above procedure every after reset needs require to modify fstab with provided entry? So moving of var on hdd will occur automatically.

But I do not have unsquashFS utility on this system and I cannot find one that can go on to fit within less than 1mb ROM free space left of this ppc device.
By the way where I can find the unsquashfs utility?

Thanks once again for your valuable guidance.

jlinkels · 03-03-2010, 12:19 PM

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