How to build squashfs tools on Mac OS X

Posted by figo on February 24, 2016

To squash/unsquash a Linux squashfs filesystem on a Mac, you can build the squashfs tools.

A few modifications of the source are required for OS X:

  • The FNM_EXTMATCH flag doesn’t exist in the fnmatch library on OS X. This just means that you can’t use glob patterns with mksquashfs.
  • The constants to figure out how many CPUs the machine has are in the sysctl header instead of the sysinfo header.
  • The C99 compiler has different semantics for the inline keyword, so inline functions should also be static.
  • Instead of llistxattr(), lgetxattr(), lsetxattr(), Apple uses a XATTR_NOFOLLOW flag on the non-link equivalent functions.

Here’s a complete download-and-build recipe:

curl -OL
tar xzvf squashfs4.2.tar.gz
cd squashfs4.2/squashfs-tools

sed -i.orig 's/FNM_EXTMATCH/0/; s/sysinfo.h/sysctl.h/; s/^inline/static inline/' mksquashfs.c unsquashfs.c

cat <<END >> xattr.h
#define llistxattr(path, list, size) \
  (listxattr(path, list, size, XATTR_NOFOLLOW))
#define lgetxattr(path, name, value, size) \
  (getxattr(path, name, value, size, 0, XATTR_NOFOLLOW))
#define lsetxattr(path, name, value, size, flags) \
  (setxattr(path, name, value, size, 0, flags | XATTR_NOFOLLOW))

sudo cp mksquashfs unsquashfs /usr/local/bin

Usage notes:

The filesystem you’re unsquashing probably has root-owned files in it, so you’ll have to use sudo to run unsquashfs as root.

The limit of open files is somewhat low on a Mac, so you’ll get a bunch of errors if you try to unsquash a whole filesystem:

write_file: failed to create file squashfs-root/path/to/file, because Too many open files

Just change the limit in the shell before running unsquashfs:

ulimit -n 2000
sudo unsquashfs filesystem.squashfs

There seems to be a bug when drawing the progress bar that causes Floating point exception, which you can workaround by using the -n flag.