[gentoo-user] 500 meg / partition (including /boot) *WITHOUT USING LVM*

[Walter Dnes]

While installing Gentoo recently, I managed to pull off a cute stunt
that...
a) minimizes wasted disk space
b) retains the ability to wipe and re-install the OS, without wiping
   user data

  I'm considering doing a Gentoo Wiki entry, if one hasn't already been
done.  First, I'll run it past the list for comments and any problems
you may find.  (Update: after a read-through, it occurs to me that I
should probably bindmount /opt similarly to /tmp, /usr, and /var).

  The example below uses /dev/sda.  Substitute as appropriate for your
system (hda or wharever)

Step 1) Partition a blank hard drive.

- partition the entire hard drive (500 gigabytes in my case) as one
  gigantic extended partition (partition 1)

- create a 500 megabyte logical linux (type 83) partition of at the
  beginning of the extended partition (partition 5).  This will be the
  / partition

- next, create a logical linux swap (type 82) partition approx twice
  the size of your ram (partition 6).

- next, create a logical linux (type 83) partition using the remainder
  of the drive (partition 7).  This will be mounted as /home.  Here's
  what my drive looks like, according to "fdisk -l"

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1       60801   488384001    5  Extended
/dev/sda5               1          62      497952   83  Linux
/dev/sda6              63         549     3911796   82  Linux swap / Solaris
/dev/sda7             550       60801   483974158+  83  Linux

  Step 2) File system creation... *WARNING* the following script wipes
all data on partitions 5, 6, and 7.  Use this only when you want to wipe
everything, *INCLUDING ALL YOUR DATA*, and start fresh.  For mounting
the drive after a reboot during install (or booting off the install CD
for rescue work) use the script in step 3.

#!/bin/bash
mke2fs /dev/sda5
mkswap /dev/sda6
mkreiserfs /dev/sda7
swapon /dev/sda6
mount /dev/sda5 /mnt/gentoo -o noatime
mkdir /mnt/gentoo/home
mount /dev/sda7 /mnt/gentoo/home -o noatime,notail
mkdir /mnt/gentoo/tmp
chmod 1777 /mnt/gentoo/tmp
mkdir /mnt/gentoo/usr
chmod 755 /mnt/gentoo/usr
mkdir /mnt/gentoo/var
chmod 755 /mnt/gentoo/var
mkdir /mnt/gentoo/home/bindmounts
mkdir /mnt/gentoo/home/bindmounts/tmp
chmod 1777 /mnt/gentoo/home/bindmounts/tmp
mkdir /mnt/gentoo/home/bindmounts/usr
chmod 755 /mnt/gentoo/home/bindmounts/usr
mkdir /mnt/gentoo/home/bindmounts/var
chmod 755 /mnt/gentoo/home/bindmounts/var
mount --bind /mnt/gentoo/home/bindmounts/tmp /mnt/gentoo/tmp
mount --bind /mnt/gentoo/home/bindmounts/usr /mnt/gentoo/usr
mount --bind /mnt/gentoo/home/bindmounts/var /mnt/gentoo/var

  Again, substitute as appropriate if your harddrive is not /dev/sda.
Let's examine the script in detail...

mke2fs /dev/sda5
mkswap /dev/sda6
mkreiserfs /dev/sda7
swapon /dev/sda6

  The first 4 commands format the partitions and activate the swapdrive.
Partition 5 really should be ext2fs for a few reasons...

  - Partition 5 will rarely be written to during normal operation; only
    when you are installing/updating programs/scripts that reside in
    /bin or /sbin so journalling isn't that important.

  - Journalling requires disk space, which we're trying to conserve.

  - Given the small size of the / partition, ext2fs is sufficient

  - ext2fs is the easiest filesystem to shrink/grow.  If you ever need
    to grow the / partition in future, you can take space from the swap
    partition.  Unless you're doing a suspend-to-swap, you can screw
    around with the swap partition with impunity.

  - partition 7 will require a (preferably journalling) filesystem that
    can handle a large partition.  I currently use reiserfs.  There are
    several competent filesystems.  The choice is yours.

mount /dev/sda5 /mnt/gentoo -o noatime
mkdir /mnt/gentoo/home
mount /dev/sda7 /mnt/gentoo/home -o noatime,notail

  The next 3 statements

  - mount partition 5 as /

  - create directory /home on partition 5

  - mount partition 7 as /home.  All physical partitions are now mounted.

mkdir /mnt/gentoo/tmp
chmod 1777 /mnt/gentoo/tmp
mkdir /mnt/gentoo/usr
chmod 755 /mnt/gentoo/usr
mkdir /mnt/gentoo/var
chmod 755 /mnt/gentoo/var

  The next 6 statements create /tmp, /usr, and /var, and set permissions.

mkdir /mnt/gentoo/home/bindmounts
mkdir /mnt/gentoo/home/bindmounts/tmp
chmod 1777 /mnt/gentoo/home/bindmounts/tmp
mkdir /mnt/gentoo/home/bindmounts/usr
chmod 755 /mnt/gentoo/home/bindmounts/usr
mkdir /mnt/gentoo/home/bindmounts/var
chmod 755 /mnt/gentoo/home/bindmounts/var

  The next 7 statements create /home/bindmounts/ on partition 7, and
then create mirrors of /tmp, /usr, and /var in /home/bindmounts, and set
permissions.

mount --bind /mnt/gentoo/home/bindmounts/tmp /mnt/gentoo/tmp
mount --bind /mnt/gentoo/home/bindmounts/usr /mnt/gentoo/usr
mount --bind /mnt/gentoo/home/bindmounts/var /mnt/gentoo/var

  And now, the connection between the directories in /home/bindmounts and
their equivalents on /, which makes the whole thing work.  If you ever
need to re-install Gentoo, or another linux distro, you can wipe the
contents of (*DO NOT* rmdir)...
/tmp
/usr
/var

  And then wipe everything in / except the 4 directories...
/home
/tmp
/usr
/var

  Step 3)

  OK, so you've set up the partitions and subdirectories.  There are
re-boots during the linux install process.  Ditto for installing a new
distro, or for doing rescue work.  Use the following script to mount the
directories...

#!/bin/bash
swapon /dev/sda6
mount /dev/sda5 /mnt/gentoo -o noatime
mount /dev/sda7 /mnt/gentoo/home -o noatime,notail
mount --bind /mnt/gentoo/home/bindmounts/tmp /mnt/gentoo/tmp
mount --bind /mnt/gentoo/home/bindmounts/usr /mnt/gentoo/usr
mount --bind /mnt/gentoo/home/bindmounts/var /mnt/gentoo/var



  The advantages of my setup...
  - a minimum of wasted disk space
  - you can create lots of files, and use almost the entire hard drive
    flexibly, because all the really variable stuff goes on the big
    partition
  - with a little care, you can wipe the OS files and keep your data,
    and re-install the same or another linux distro.

  Disadvantages...
  - "find" will show duplicate results if the target file physically
    exists in /home/bindmounts
  - in Gentoo, /etc/localtime is a physical file, not a symlink into
    /usr/share/zoneinfo.  If it is a symlink in your distro, scripts
    that execute early in the boot process might get confused about what
    time it is.

-- 
Walter Dnes <waltdnes@××××××××.org> In linux /sbin/init is Job #1
Q. Mr. Ghandi, what do you think of Microsoft security?
A. I think it would be a good idea.
-- 
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