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?
On a virtualized server running Ubuntu 10.04, df reports the following:
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 7.4G 7.0G 0 100% /
none 498M 160K 498M 1% /dev
none 500M 0 500M 0% /dev/shm
none 500M 92K 500M 1% /var/run
none 500M 0 500M 0% /var/lock
none 500M 0 500M 0% /lib/init/rw
/dev/sda3 917G 305G 566G 36% /home
This is puzzling me for two reasons: 1.) df says that /dev/sda1, mounted at /, has a 7.4 gigabyte capacity, of which only 7.0 gigabytes are in use, yet it reports / being 100 percent full; and 2.) I can create files on / so it clearly does have space left.
Possibly relevant is that the directory /www is a symbolic link to /home/www, which is on a different partition (/dev/sda3, mounted at /home).
Can anyone offer suggestions on what might be going on here? The server appears to be working without issue, but I want to make sure there's not a problem with the partition table, file systems or something else which might result in implosion (or explosion) later.
How do you delete all partitions on a device from the command line on Linux (specifically Ubuntu)? I tried looking at fdisk, but it presents an interactive prompt. I'm looking for a single command, which I can give a device path (e.g. /dev/sda) and it'll delete the ext4, linux-swap, and whatever other partitions it finds. Essentially, this would be the same thing as if I were to open GParted, and manually select and delete all partitions. This seems fairly simple, but unfortunately, I haven't been able to find anything through Google.
Sometimes, when resizing or otherwise mucking about with partitions on a disk, cfdisk will say:
Wrote partition table, but re-read table failed. Reboot to update table.
(This also happens with other partitioning tools, so I'm thinking this is a Linux issue rather than a cfdisk issue.) Why is this, and why does it only happens sometimes, and what can I do to avoid it?
Note: Please assume that none of the partitions I am actually editing are opened, mounted or otherwise in use.
Update:
cfdisk uses ioctl(fd, BLKRRPART, NULL) to tell Linux to reread the partition table. Two of the other tools recommended so far (hdparm -z DEVICE, sfdisk -R DEVICE) does exactly the same thing. The partprobe DEVICE command, on the other hand, seems to use a new ioctl called BLKPG, which might be better; I don't know. (It also falls back on BLKRRPART if BLKPG fails.)
BLKPG seems to be a "this partition has changed; here is the new size" operation, and it looked like partprobe called it individually on all the partitions on the device passed, so it should work if the individual partitions are unused. However, I have not had the opportunity to try it.
I'm running Ubuntu, and want to find out the UUID of a particular filesystem (not partition). I know I can use e2label /dev/sda1 to find out the filesystem label, but there doesn't seem to be a similar way to find the UUID.