====== Fstab Configuration ======

The ''/etc/config/fstab'' configuration file defines static file systems and swap partitions that should be activated at boot. Please read the [[#Notes]] before proceeding.

:!: The package **''block-mount''** is required: 
  - Install <code>opkg update
opkg install block-mount</code>
  - enable (make it start automatically on every boot up) <code>/etc/init.d/fstab enable</code>
  - and start (right now) <code>/etc/init.d/fstab start</code>

Whenever you change your configuration, restart this to make it take effect: <code>/etc/init.d/fstab restart</code>


===== Sections =====
The configuration file can consist of sections defining file systems to be mounted and swap partitions to be activated.

==== Automount ====
There is one ''global'' section named ''automount'' which defines the hotplug automounting behaviour.

This example is included by default:
| ''config 'global' 'automount'
        option 'from_fstab' '1'
        option 'anon_mount' '1'
'' |

The ''automount'' section contains these settings:
^ Name ^ Type ^ Required ^ Default ^ Description ^
| ''from_fstab'' | boolean | no | ''1'' | Whether to use ''mount'' sections when doing hotplug mounts |
| ''anon_mount'' | boolean | no | ''1'' | When using hotplug mounts, whether to automatically mount filesystems not defined in a ''mount'' section under /mnt/$device |

==== Autoswap ====
There is one ''global'' section named ''autoswap'' which defines the hotplug auto swap behaviour.

This example is included by default:
| ''config 'global' 'autoswap'
        option 'from_fstab' '1'
        option 'anon_swap' '0''' |

The ''autoswap'' section contains these settings:
^ Name ^ Type ^ Required ^ Default ^ Description ^
| ''from_fstab'' | boolean | no | ''1'' | Whether to use ''swap'' sections when doing hotplug swap on |
| ''anon_swap'' | boolean | no | ''0'' | When using hotplug swapon, whether to automatically swapon devices not defined in a ''swap'' section |


==== Mounting Filesystem ====
Each ''mount'' section defines a filesystem to be mounted at boot. Filesystems must be formatted before they can be used.

This example is included by default:
| ''config 'mount'
        option 'target'   '/home'
        option 'device'   '/dev/sda1'
        option 'fstype'   'ext4'
        option 'options'  'rw,sync'
        option 'enabled'  '0'
        option 'enabled_fsck' '0''' |

The ''mount'' section contains these settings:
^ Name ^ Type ^ Required ^ Default ^ Description ^
| ''device'' | string | yes or ''uuid'' or ''label'' | //(none)// | Device (partition) to mount the filesystem from.  If ''uuid'' or ''label'' are specified, they are used, rather than ''device''. |
| ''uuid'' | string | yes or ''device'' or ''label'' | //(none)// | UUID of device (partition) to mount the filesystem from, as shown by ''blkid''.  If ''uuid'' is present in the ''mount'' section, it is used in preference to ''label'' or ''device''. |
| ''label'' | string | yes or ''device'' or ''uuid'' | //(none)// | LABEL of device (partition) to mount the filesystem from, as shown by ''blkid''.  If ''uuid'' is present in the ''mount'' section, it takes precedence.  ''label'' takes precedence over ''device''.|
| ''enabled'' | boolean | no | ''1'' | Whether to mount this filesystem automatically at boot. |
| ''fstype'' | string | no | ''auto'' | Type of the filesystem (i.e. ''ext3''). [[https://forum.openwrt.org/viewtopic.php?id=32812|remote file systems]] |
| ''options'' | string | no | ''rw'' | Mount options for this filesystem. |
| ''target'' | string | yes | //(none)// | Target directory to mount the filesystem onto.  After [[https://dev.openwrt.org/changeset/25787/trunk|r25787]] specifying '''/overlay''' here means this filesystem will be mounted as the overlay-based rootfs, while after [[https://dev.openwrt.org/changeset/26109/trunk|r26109]] specifying '''/''' here means the filesystem will be mounted as regular rootfs (that is not overlay-based). (see [[doc:howto:extroot|extroot]]) |
| ''enabled_fsck'' | boolean | no | ''0'' | Whether to automatically check for/repair errors before mounting the filesystem. |
| ''is_rootfs'' | boolean | no | ''0'' | »Please read the particular article **[[doc:howto:extroot]]** for this functionality!«\\ {{:meta:icons:tango:48px-outdated.svg.png?nolink&24}} deprecated after [[https://dev.openwrt.org/changeset/25787/trunk|r25787]].\\ **Before r25787 it is required for block-extroot mounts ** |

==== Adding Swap Partitions ====

Each ''swap'' section defines a swap partition to be activated at boot.\\
:!: Swap partitions must be formatted before they can be used and the ''swap-utils'' package needs to be installed!\\
:!: Swap partitions must be first defined using the ''mkswap /dev/device'' command!

This example is included by default:
| ''config 'swap'
        option 'device'   '/dev/sda2'
        option 'enabled'  '0''' |

The ''swap'' section contains these settings:
^ Name ^ Type ^ Required ^ Default ^ Description ^
| ''device'' | string | yes or ''uuid'' or ''label'' | //(none)// | Device (partition) to mount the swap from. ''uuid'' and ''label'' take precedence |
| ''uuid'' | string | yes or ''device'' or ''label'' | //(none)// | UUID of device (partition) to mount the swap from, as shown by blkid.  If uuid is present in the ''mount'' section, it is used in preference to ''label'' or ''device''. |
| ''label'' | string | yes or ''device'' or ''uuid'' | //(none)// | LABEL of device (partition) to mount the swap from, as shown by blkid.  If uuid is present in the ''mount'' section, it takes precedence.  ''label'' takes precedence over ''device''.|
| ''enabled'' | boolean | no | ''1'' | Whether to activate this swap partition automatically at boot. |


==== The right amount of SWAP ====

If you ask people or search the net, you will find as a general rule of thumb //double RAM// for machines with 512MiB of RAM or less than, and //same amount as RAM// for machines with more. But this very rough estimate does apply for your embedded device! Be aware that there are exactly two differences between RAM and SWAP, that matter: the **access time** and the **price**. A CUPS spooling server will run just fine, when only SWAP is available, whereas some applications may perform very poorly when their data it stored on the SWAP rather then being kept in the "real" RAM. The decision which data is kept in the RAM and which is stored on the SWAP is made by the system. As explained here [[http://wiki.debianforum.de/LinuxSpeichermanagement#head-9146624b4965952684a04aeaad765ab62896c711|Debian Forum (german)]] since Kernel 2.6 you can define the ''swapiness'' of your system:

<code>root@OpenWrt:~# sysctl -w vm.swappiness=60
root@OpenWrt:~# echo 60 > /proc/sys/vm/swappiness</code>


In contrast to other operating systems, Linux makes ample use of memory, so that your system runs smoother and more efficiently. If memory is then needed by an application, the system will unload stuff again, and make memory available. For OpenWrt, let us just say to use as much SWAP-Space as //needed// by your applications running. If this should not perform well, because of the poor access time, it would not help to decrease the amount of SWAP, but only to run fewer services at the same time or increase the amount of RAM with a soldering iron ;-)

OpenWrt vanilla will run just fine, with no SWAP at all. But after you installed a couple of applications, you could try to mount a SWAP-Partition and see what is does for you. Do not worry, you can not brake anything by doing that. The manual commands are ''swapon /dev/sdaX'' to mount respectivly ''swapoff /dev/sdaX'' to unmount. Type in ''free'' to see the usage of memory:

<code>root@OpenWrt:~# free
              total         used         free       shared      buffers
  Mem:        29484        28540          944            0         1116
 Swap:       524280         2336       521944
Total:       553764        30876       522888</code>

In this example there is 32MiB of RAM and 512MiB of SWAP. SWAP is a SWAP-formated 512MiB-Partition on a large USB-Harddisk. In this example, only 2MiB are being used! And you do not see here, that actually half the RAM is being wasted for a TMPFS-Drive. Use ''df'' to see that:
<code>root@OpenWrt:~# df  
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/root                 1280      1280         0 100% /rom
tmpfs                    14744       116     14628   1% /tmp       <= //Up to 14MiB of RAM may be used here, the//
tmpfs                      512         0       512   0% /dev         //tmpfs partitions grow and shrink with usage!//
/dev/mtdblock3            5440      4988       452  92% /overlay
mini_fo:/overlay          1280      1280         0 100% /
/dev/sda2              2709204     86276   2485284   3% /mnt/sda2
/dev/sda3              7224600    147320   6710196   2% /mnt/sda3</code>

In this example, it would probably perform better, to mount the /tmp-directory on the USB-Harddisk and not use TMPFS at all, rather than using a 512MiB-Swap Partition. But you can also see, that ''overlay'' has only 8% space left to install programs on. So in this example it would be even better to use the exroot option. See [[doc:howto:extroot]]
for that.

===== Troubleshooting =====

====Sleep before startup====
I installed the packages, enabled the fstab, and changed my fstab config file. When I restart, the drive does NOT show up.  I can issue an ''/etc/init.d/fstab start'' and I get an error that it can't find a file (''/tmp/fstab'') but the drive mounts. I took the advice from this posting https://forum.openwrt.org/viewtopic.php?id=27210 and put "sleep 15" in the start function of the ''/etc/init.d/fstab'' file.  (I'm using a USB stick) That fixed the problem.

| ''start() {
        sleep 15
        config_load fstab
        mkdir -p /var/lock
        lock /var/lock/fstab.lck
        #echo '# WARNING: this is an auto generated file, please use uci to set defined filesystems' > /etc/fstab
        lock -u /var/lock/fstab.lck
        config_foreach do_mount mount
        config_foreach do_swapon swap
}'' |

https://forum.openwrt.org/viewtopic.php?id=28311

===== Notes =====
|''block-mount'': Scripts used to mount and check block devices (file systems and swap), as well as hotplug scripts to automount and check block devices when hotplug event (e.g. from plugging in a device) occurs. Also includes preinit scripts for mounting a block device as the root filesystem. This allows one to have the root filesystem on devices other than the built in flash device.|

| {{:meta:icons:tango:48px-outdated.svg.png?nolink}} | As of [[https://dev.openwrt.org/changeset/26314/trunk|r26314]] ''block-extroot'' and ''block-hotplug'' have been merged with **''block-mount''**.  |
| {{:meta:icons:tango:48px-outdated.svg.png?nolink}} | In the OpenWrt 'Backfire' 10.03 release there is a bug. Solution is: ''vi /etc/init.d/fstab'' and put a ''#'' in front of the line: <code>echo '# WARNING: this is an auto generated file, please use UCI to set defined filesystems' > /etc/fstab</code> This creates the file ''/etc/fstab'' and thus prevents creating a symlink to ''/tmp/fstab''. In order for UCI to work, there need to be symlink! In case the bug has already taken place, delete /etc/fstab and then type this code to busybox. <code>ln -s /tmp/fstab /etc/fstab</code> It will create a symlink to the /tmp/fstab file, fixing the bug completely. |