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Two ways to improve OS-X...

I found this excellent article, Mac OS X SSD tweaks by Ricardo Gameiro, and have stolen two of the ideas for my non-SSD MacBook Pro laptop. I’ll cover all three, though, since I don’t agree with his hibernation trick.

Turn off “atime”

This is pretty simple. Setting noatime turns off recording of when files are accessed. I’ve never found a usage for the recording of file accesses. However, you may have a use for this behavior, so be warned.

To turn off atime then just dump this XML into /Library/LaunchDaemons/com.nullvision.noatime.plist.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
<plist version="1.0">
        <true />

Turn off hibernate

In the article, he suggests turning off hibernate altogether. I don’t like this. The hibernate is really handy if something goes wrong and you loose all your power.

There are two ways OS-X goes to sleep: suspend and hibernate.

The first is suspend. Information on the system state is stored to ram and the CPU is stopped. This is really fast to sleep and really fast to restore. The downside is that if the system looses power, it cannot restore; the ram is wiped clean.

The second is hibernate. Information on the system state is stored to disk and the CPU is stopped. The system is powered off. On restart, the state is read from disk and the system restarts as normal. This is slow to sleep and restore, but if power is lost, the system state is still safe.

OS-X, for laptops, does both. This means it is slow to shutdown, but fast to restore.

Obviously, if you are using SSD or if you want shutdowns to be fast (like I do, since I tend to shut my lid and carry around my laptop immediately), then you really don’t want hibernation to happen unless you really need it.

So I use SmartSleep by Patrick Stein. The only time my laptop hibernates is when the power is low. The best of both worlds.

Storing /tmp/ in ram

This recipe is nearly the same as Ricardo’s suggestion. I just added the code from Patrick Gibson’s comment.

This is two part; you need to create a shell script and a .plist file.

The shell script goes in /var/root/ You must do a chmod a+x /var/root/ afterwards.


set -eu


ramfs_size_sectors=$(( ${ramfs_size_mb} * 1024 * 1024 / 512 ))
ramdisk_dev=$(hdid -nomount ram://${ramfs_size_sectors} | cut -d ' ' -f 1)
newfs_hfs -v 'Volatile HD' "${ramdisk_dev}"
mkdir -p "${mount_point}"
mount -o noatime -t hfs "${ramdisk_dev}" "${mount_point}"

# hide the volume from the Finder
if [ -e /usr/bin/SetFile ]; then
 /usr/bin/SetFile -a V "${mount_point}"

# fix permissions
chown root:wheel "${mount_point}"
chmod 1777 "${mount_point}"


Next you need to drop a .plist file in /Library/LaunchDaemons/com.nullvision.ramfs.plist.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "">
<plist version="1.0">
        <true />

I don’t recommend moving any caches or anything, as he mentions at the end of the article. Just having /tmp/ (aka /private/tmp/) will be an advantage. Well, except the X-Code thing. That’s probably useful.


Addendum: Reverting /tmp

I discovered that iDefrag2 needs to have /tmp be a real file-system to do it’s “No bootable CD/DVD required!” trick. After hashing it out with a helpful developer (Thanks, Chris!) we tracked it down to putting /tmp into ram.

To undo it, run these commands as root:

rm /Library/LaunchDaemons/com.nullvision.ramfs.plist
rm /var/root/
mkdir /private/tmp2
mv /private/tmp /private/tmp2 ; mv /private/tmp2 /private/tmp
chown root:wheel /private/tmp
chmod 1777 /private/tmp

You should reboot immediately after this change.

After reboot, verify that /tmp and /private/tmp are set up correctly:

$ ls -ald /tmp /private/tmp
drwxrwxrwt 18 root wheel 612 Jun 16 09:47 /private/tmp/
lrwxr-xr-x  1 root admin  11 Jun 16 09:23 /tmp -> private/tmp/

Important: Verify that the /tmp symlink points to private/tmp not /private/tmp!


Gravatar for brandon zylstra
Brandon Zylstra

The only use for atime that I know of, other than satisfying your curiosity, is mutt: mutt uses it, apparently to keep track of when/whether you’ve read an e-mail message.

I haven’t tested it, but this is according to a presenter at Windy City Rails, giving tips for dramatically speeding up automated tests for Rails & Ruby applications.

Gravatar for docwhat

That is only true for mbox format, I think. Maildir has flags in the filename and mutt scans those.

Gravatar for k

just dont try to run defrag on an SSD drive! Not only it is useless, but also dangerous for your drive! (even if yo believe defrag is useful on a normal drive which used to be the case 15 years ago).

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