Add read only root page

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+title: Read Only Root
+linktitle: ro-root
+parent: Home
+ctime: 2012-08-02
+
+For GNU/Linux desktop installations, I prefer to have the root filesystem,
+which mounts to /, be mostly read-only.  This means that /home, /var and /tmp
+need to be mounted elsewhere.  The benefits of this approach are several, but
+two in particular stand out for desktop use cases.
+
+ * It is much easier to do a clean install the OS.  User data in /home, and
+   in some cases application data in /var, need not be backed up and restored
+   in the process.  Of course recent backups should still be available.
+ * A root fs that is rarely written to is a good candidate for SSD (solid state
+   disk) storage.  This allows one the performance benefit of SSD while
+   mitigating a critical deficiency.  Current SSD technology is not nearly
+   as reliable as mechanical disk in read/write environments, so reducing
+   writes to SSD is a productive strategy.
+
+Placing /home on a separate partition is easy, and GNU/Linux desktop installers
+have supported this for some time.  And thanks to the recent introduction of
+/run (see [here](http://lwn.net/Articles/436012/) to learn more), migrating
+/var to a separate filesystem is now pretty easy for desktop installs.
+
+Of course, with multiple partitions, there is the issue of what to do if one of
+them fills up.  A common solution is to use LVM.  Volumes are given minimal
+practical sizes, and then incrementally grown as required.  LVM works fine on
+the desktop, but requires a bit more knowledge and effort to administer.
+
+A simpler solution is to use bind mounts.  By bind mounting /var from /home/var
+and /tmp from /home/tmp, all user, variable and temporary data are on a single
+partition.  The root partition will be nearly static in content and size.  I
+currently use a 25 GB root partition on desktop installs, and that filesystem is
+generally only about 25% full, even with a large number of development tools
+installed.  A swap partition is present of course, and the rest of the available
+hard drive storage space is assigned to the home partition, which now holds the
+contents of /var and /tmp.  Essentially, /home, /var and /tmp share a common
+large pool of storage, so there is less need for a volume manager.  I am finding
+this configuration to be quite optimal for developer desktops at my company.
+
+# Using bind mounts in a new installation
+
+These notes assume Xubuntu 12.04 desktop i386 installation, but a similar
+process should work for other distributions and versions.
+
+ * Boot from the xubuntu 12.04 desktop CD
+ * Run the installation
+ * Use a custom configuration when asked
+ * At least three partitions are required: root, swap and home
+ * Proceed with installation until the installer asks to reboot to continue
+
+Before rebooting, access a shell and type the following commands
+
+    cd target # where the new root filesystem is currently mounted
+    cp -a var home/var # copy var to its new storage location
+    mv var var.old # can remove later
+    mkdir var # Need some dirs and symlinks during boot for some OSes
+    ln -s /run var/run
+    ln -s /run/lock var/lock
+    cp -a tmp home/tmp # copy tmp to its new storage location
+    mv tmp tmp.old
+    mkdir tmp
+    vi etc/fstab # add the following 2 bind mounts to end of /etc/fstab
+        /home/var /var bind defaults,bind,noatime,mode=0755 0 0
+        /home/tmp /tmp bind defaults,bind,noatime,mode=1777 0 0
+    sync
+
+Now allow the installer to reboot.  The system should boot up using the bind
+mounts for /var and /tmp, so their contents will actually be stored in the home
+partition at locations /home/var and /home/tmp, respectively.  Once the system
+appears to be working OK, you may remove the /var.old and /tmp.old directories.
+
+# Upgrading to use bind mounts
+
+First, boot from a recovery or live CD, then run commands like the following
+commands.
+
+    mkdir /mnt
+    mount /dev/sda1 /mnt # replace /dev/sda1 with dev for your root
+    mount /dev/sda2 /mnt/home # replace /dev/sda2 with dev for your home
+    cd /mnt
+    cp -a var home/var # copy /var to its new storage location
+    mv var var.old # can remove later
+    mkdir var # Need some dirs and symlinks during boot for some OSes
+    ln -s /run var/run
+    ln -s /run/lock var/lock
+    cp -a tmp home/tmp # copyt /tmp to its new storage location
+    mv tmp tmp.old # can remove later
+    mkdir tmp
+    vi etc/fstab # add the following 2 bind mounts to end of /etc/fstab
+        /home/var /var bind defaults,bind,noatime,mode=0755 0 0
+        /home/tmp /tmp bind defaults,bind,noatime,mode=1777 0 0
+    sync
+
+Now remove the CD and reboot.  You should be using bind mounts.  Once the system
+appears to be working OK, you may remove the /var.old and /tmp.old directories.