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What is the recommended size for a Linux /boot partition?

And is it safe to not have a /boot partition?

I see some servers don't have a /boot partition while some servers have a 128 MB /boot partition. I am a little confused. Is /boot partition necessary? If it is, how large should it be?

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7 Answers 7

up vote 16 down vote accepted

These days, 100 Megabytes or 200 Megabytes is the norm.

You do not need to have a /boot partition. However, it's good to have for flexibility reasons (LVM, encryption, BIOS limitations).

Edit:

The recommended size has been increased to 300MB-500MB.

Also see: http://superuser.com/questions/66015/installing-ubuntu-do-i-really-need-a-boot-parition

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If you want to use btrfs you need to have a boot partition. –  josten May 4 at 14:44

I just installed Ubuntu 13.10 with a 105MB /boot. It installed fine, but after it rebooted I did the updater, it said that there was not enough space. Wanted around another 196MB for the upgrade, must be a kernel upgrade or something. So had to reinstall with a bigger /boot. Went for 500MB and that seemed to work. Good thing it doesn't take long to do a new install :)

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Ubuntu doesn't always remove old kernels after an upgrade. You need to do that yourself. Otherwise it may keep several of them around for a long time. –  Matt Mar 24 at 2:38

I always use 100MB as a rule when I'm building systems. I suppose if you're going to be testing out tons of different kernels (or building your own custom kernels) you may want a larger one, but 100MB is enough for most people. Also, as mentioned, having a separate boot partition is a good idea for a bunch of reasons.

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2  
Current distributions want 200MB+. –  ewwhite Jun 29 '12 at 2:20

It's mostly a function of how many kernels you have installed, and the size of their initrds.

For a 3.0 series kernel, initrd runs about 13 MB. For early 2.6 kernels, this was 3.4 MB. So, if you plan on keeping more than a few kernels around, you'll need at least a couple hundred MB.

How much and whether or not this applies to you depends on your use case. If you multi-boot, test kernels, and/or upgrade frequently, you could run out of space on a 100 MB /boot partition quickly. If you don't do any of these things, it's probably going to be sufficient.

There are very few reasons to skimp on storage (it's cheap, BIOS, mount, and bootloader restrictions on blocks are mostly a thing of the past), and I'm seeing a marked growth in kernel resources with time, so the safe bet would be ~250 MB - 1 GB for now. I still generally prefer a separate /boot partition for control and isolation, though this has almost entirely become a matter of taste (RAID devices would be one obvious exception, LVM and encryption as well as noted by others).

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It also differs distribution from distribution. For example for Fedora minimum is 250MB[1] and 500MB is default and if you plan to (pre)upgrade in the future 500MB is required[2]. If space is not a problem I would go for 1GB to prevent shuffling partitions later as I had to do when upgrading recently.

[1] http://docs.fedoraproject.org/en-US/Fedora/16/html/Installation_Guide/s2-diskpartrecommend-x86.html [2] http://fedoraproject.org/wiki/How_to_use_PreUpgrade#Not_enough_space_in_.2Fboot

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I tend to create a 1GB /boot. I leave a livecd image which has various repair tools in my /boot. I mostly do this for systems that at the remote sites I support. With the right configuration, and enough memory, grub2 can boot the image without extracting the contents. A couple times I have talked remote staff into rebooting the system to the livecd image and starting networking/ssh on a system that was having issues so I could connect and repair things.

This certainly isn't required, or even common.

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Which Live CD do you prefer in these cases? –  ewwhite Nov 25 '11 at 12:09
1  
For me the distro of choice is SystemRescueCD and Finnix is another nice one. –  Martian Nov 25 '11 at 13:10
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You sir, are awesome. –  SpacemanSpiff Nov 25 '11 at 13:23
    
I use PXE for the rescue and provisioning stuff. I can upgrade the rescue stuff much faster and without fear that I can break a running system. –  Mircea Vutcovici Nov 25 '11 at 15:53
    
@zoredache I'm installing arch linux on my external hard disk for work purpose, I would like to add live image as you said you did, for rescue, can you please point me any links how to do that? –  pahnin Jul 5 '13 at 6:39

What is the recommended size for a linux /boot partition?

The /boot parition contains the GRUB configuration, the kernel with their System.map, ... I think ~ 100MB is enough.

And is it safe to not have a /boot partition?

Yes. But a separate /boot partition has some advantages:

  • as a rescue partition
  • rootfs is on a LVM, RAID, is encrypted, or unsupported by GRUB
  • may be saves a few seconds of boot time
  • ...
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I've been surprised relatively recently with a bios that couldn't access above 1023(?) cylinders, too. –  Random832 Nov 25 '11 at 7:54
    
@quanta how 'may be saves a few seconds of boot time'? –  Alessandro Pezzato Nov 25 '11 at 13:28
    
Because usually /boot is at the beginning of the disk, which is usually on the outer sectors has less chances to get fragmented and the path is smaller (less directory reads), it is usually a primary partition (no need to read the logical partition chain). But I doubt that you gain more than 1s. –  Mircea Vutcovici Nov 25 '11 at 15:49

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