Unix: fast 'remove directory' for cleaning up daily builds

Question

Is there a faster way to remove a directory then simply submitting

rm -r -f *directory*

? I am asking this because our daily cross-platform builds are really huge (e.g. 4GB per build). So the harddisks on some of the machines are frequently running out of space.

This is namely the case for our AIX and Solaris platforms.

Maybe there are 'special' commands for directory remove on these platforms?

PASTE-EDIT (moved my own separate answer into the question):

I am generally wondering why 'rm -r -f' is so slow. Doesn't 'rm' just need to modify the '..' or '.' files to de-allocate filesystem entries.

something like

mv *directory* /dev/null

would be nice.

Answer 1

I think that actually there is nothing else than "rm -rf" as you quoted to delete your directories.

to avoid doing it manually over and over you can cron daily a script that recursively deletes all the build directories of your build root directory if they're "old enough" with something like :

find <buildRootDir>/* -prune -mtime +4 -exec rm -rf {} \;

(here mtime +4 indicates "any file older than 4 days)

Another way would be to configure your builder (if it allows such things) to crush the previous build with the current one.

Answer 2

For deleting a directory from a filesystem, rm is your fastest option. On linux, sometimes we do our builds (few GB) in a ramdisk, and it has a really impressive delete speed :) You could also try different filesystems, but on AIX/Solaris you may not have many options...

If your goal is to have the directory $dir empty now, you can rename it, and delete it later from a background/cron job:

mv "$dir" "$dir.old"
mkdir "$dir"
# later
rm -r -f "$dir.old"

Another trick is that you create a seperate filesystem for $dir, and when you want to delete it, you just simply re-create the filesystem. Something like this:

# initialization
mkfs.something /dev/device
mount /dev/device "$dir"


# when you want to delete it:
umount "$dir"
# re-init
mkfs.something /dev/device
mount /dev/device "$dir"

Answer 3

On AIX at least, you should be using LVM, the logical volume manager. All our systems bundle all the physical hard drive into a single volume group and then create one big honkin' file system out of that.

That way, you can add physical devices to your machine at will and increase the size of your file system to whatever you need.

One other solution I've seen is to allocate a trash directory on each file system and use a combination of mv and a find cron job to tackle the space problem.

Basically, have a cron job that runs every ten minutes and executes:

rm -rf /trash/*
rm -rf /filesys1/trash/*
rm -rf /filesys2/trash/*

Then, when you want your specific directory on that file system recycled, use something like:

mv /filesys1/overnight /filesys1/trash/overnight

and, within the next ten minutes your disk space will start being recovered. The filesys1/overnight directory will immediately be available for use even before the trashed version has started being deleted.

It's important that the trash directory be on the same filesystem as the directory you want to get rid of, otherwise you have a massive copy/delete operation on your hands rather than a relatively quick move.

Answer 4

If rm -rf is slow, perhaps you are using a "sync" option or similar, which is writing to the disk too often. On Linux ext3 with normal options, rm -rf is very quick.

One option for fast removal which would work on Linux and presumably also on various Unixen is to use a loop device, something like:

hole temp.img $[5*1024*1024*1024]  # create a 5Gb "hole" file
mkfs.ext3 temp.img
mkdir -p mnt-temp
sudo mount temp.img mnt-temp -o loop

The "hole" program is one I wrote myself to create a large empty file using a "hole" rather than allocated blocks on the disk, which is much faster and doesn't use any disk space until you really need it. http://sam.nipl.net/coding/c-examples/hole.c

I just noticed that GNU coreutils contains a similar program "truncate", so if you have that you can use this to create the image:

truncate --size=$[5*1024*1024*1024] temp.img

Now you can use the mounted image under mnt-temp for temporary storage, for your build. When you are done with it, do this to remove it:

sudo umount mnt-temp
rm test.img
rmdir mnt-temp

I think you will find that removing a single large file is much quicker than removing lots of little files!

If you don't care to compile my "hole.c" program, you can use dd, but this is much slower:

dd if=/dev/zero of=temp.img bs=1024 count=$[5*1024*1024]  # create a 5Gb allocated file

Answer 5

rm -r directory works by recursing depth-first down through directory, deleting files, and deleting the directories on the way back up. It has to, since you cannot delete a directory that is not empty.

Long, boring details: Each file system object is represented by an inode in the file system, which has file system-wide, flat array of inodes.[1] If you just deleted directory without first deleting its children then the children would remain allocated, but without any pointers to them. (fsck checks for that kind of thing when it runs, since it represents file system damage.)

[1] That may not be strictly true for every file system out there, and there may be a file system that works the way you describe. It would possibly require something like a garbage collector. However, all the common ones I know of act like fs objects are owned by inodes, and directories are lists of name/inode number pairs.