Question: Proper way to mount system cache directories to TmpDisk?

[DawnLiExp]

macOS 13.7.5
TD v2.1.0

For example:

• /Users/username/Library/Caches
• /var/folders/vf/cs4l7qys3n7dd5c8r1q2sq400000gn/T

I tried creating a 1GB TmpDisk and symlinking it to /Users/username/Library/Caches. It seemed to work initially, but when I rebooted, the system got stuck at the desktop.

How should I do this properly? Thanks!

[DawnLiExp]

I've considered some approaches – could delaying TmpDisk's startup be a solution? For example:

#!/bin/bash
sleep 10  # Wait for system to stabilize
open -a /Applications/TmpDisk.app --args -name=CacheDisk -size=1024
sleep 2
rm -f ~/Library/Caches
ln -s /Volumes/CacheDisk ~/Library/Caches

[imothee]

Hi @DawnLiExplorer I'll need to do a bit of testing but I expect that directly symlinking to the volume won't work because that volume doesn't exist on startup and will cause issues (like you said getting stuck at desktop).

My guess would be to either mount a TmpDisk system on /Users/username/Library/Caches which would create the virtual mounting on top of the existing folder or symlink to a known folder that will be the mount point for the TmpDisk when it starts.

The biggest issue with this is right now I delete the underlying mount directly for TmpFS and I don't like the idea of moving mounts outside of the existing sandboxes of /Volumes and ~/.tmpdisk

Would something like a flag to not delete the folder work, that way you could have an always there folder at

~/.tmpdisk/cache
then you could synlink /Users/username/Library/Caches to ~/.tmpdisk/cache

TmpFS mounts would then mount over the existing folder and give you direct access to the tmpdisk. The only gap would be any files cached while the TmpDisk wasn't mounted would be hidden in ~/.tmpdisk/cache when it wasn't running.

Let me play with a few setups and see what the simplest way to get this working is. I haven't heard of anyone else doing this so making it a top level setting to directly mount isn't my first choice

[DawnLiExp]

Thank you for your patience and detailed explanations. I'm pretty new to TmpDisk and still getting the hang of it. I realize my request might be niche or even unreasonable, so please don't let it distract you from TmpDisk's core development direction. Keep up the great work!

For the past ten years, I've been using an app called RAMDisk Manager to set macOS's "Caches" and "Temporary" folders to RAM. The app stopped being developed a decade ago, but surprisingly, it still works perfectly even through major system changes like 10.13 (APFS), 10.15 (64-bit), and now on macOS 15.

But I know it will eventually be phased out by newer OS, which is why I'm looking for a modern alternative.

[imothee]

Hi @DawnLiExplorer I'm happy to look into this. I just checked my cache folder and it's 33gb so I'm wondering do you also need the usage monitoring and the recreate disk or is just mounting the folders to the right mount points enough?

[imothee]

@DawnLiExplorer I've been trying to mount a disk on top of ~/Library/Caches and the operating system won't let me. Do you know how it was setup wth Ramdisk Manager? Was it creating a mount on top of the existing folder, deleting the folder and mounting or was it creating a mount and symlinking to it? I don't have a copy and can't find one to replicate but running hdiutil and mount even with sudo gives me an oepration not permitted.

[DawnLiExp]

Hi @DawnLiExplorer I'm happy to look into this. I just checked my cache folder and it's 33gb so I'm wondering do you also need the usage monitoring and the recreate disk or is just mounting the folders to the right mount points enough?

Looks like we have quite different usage habits 😄, Mounting Caches to RAM might not be standard practice, so I suspect this need might deviate from TmpDisk's development direction.

I regularly add frequently r/w directories like ~/Library/Caches to ramdisk:

• Use as temp storage for downloads/unpacking

• Reduce filesystem fragmentation

• Improve system cache efficiency

• Minimize SSD writes

I even made a script (packaged with Platypus) that sits in my Dock:

EMPTY_DIR=$(mktemp -d)
rsync -a --delete "$EMPTY_DIR/" "/Users/username/Library/Caches/"
rsync -a --delete "$EMPTY_DIR/" "..."
rm -rf "$EMPTY_DIR"
osascript -e 'display notification "..."'

I trigger it via BetterTouchTool hotkeys or dock clicks to clear the cache directories between work sessions. Usage monitoring would be nice (like RAMDisk Manager's alerts when disk is full), but not essential.

@DawnLiExplorer I've been trying to mount a disk on top of ~/Library/Caches and the operating system won't let me. Do you know how it was setup wth Ramdisk Manager? Was it creating a mount on top of the existing folder, deleting the folder and mounting or was it creating a mount and symlinking to it? I don't have a copy and can't find one to replicate but running hdiutil and mount even with sudo gives me an oepration not permitted.

It just occurred to me - could this be SIP-related? From what I remember, RAMDisk Manager worked with SIP enabled (just didn't auto-hide to status bar properly), though I'd need to verify.

Many users of classic Mac utilities (like TotalFinder, theme mods, etc.) dislike SIP. Personally as a user I don't mind fighting Apple's restrictions, but for development software it might be different.

Not sure about RM's implementation, but I've observed that:

• TmpDisk's ramdisks appear in RM's interface
• RM's ramdisks don't show in TmpDisk's "Current TmpDisks"

So they share some mechanisms but aren't identical.

After some Googling, RM is available here(trial). Or I can email you the version I'm currently using if it helps with your research.

[imothee]

Hi @DawnLiExplorer I'm using MacOS 15.4.1 and I cannot mount the caches folder from RamDisk either. It's definitely something from SIP that's not allowing me to edit any of the system protected folders.

I'll keep looking for workarounds but wanted to update you.

[DawnLiExp]

@imothee Thanks for the update, and really appreciate you looking into it!

I just tested on:

iMac19,1
OS 15.4 (booted from an external backup drive)
TmpDisk 2.2.0-beta

Method 1:
Tried creating a tmpdisk with the mount point at ~/Library/Caches — didn’t work, whether SIP is on/off.

Method 2:

1. Created a tmpdisk named CacheDisk, 1GB, all other options default.

2. sudo rm -rf ~/Library/Caches && ln -sf /Volumes/CacheDisk ~/Library/Caches

It worked — but ~/Library/Caches is now a symlink, rebooting the system will get it stuck after login. ⚠️

To recover:

sudo rm -rf ~/Library/Caches

The system should recreate it. If not:

mkdir ~/Library/Caches
chmod 700 ~/Library/Caches

Extra
Not sure how RAMDisk Manager works exactly, but it auto-mounts after reboot just fine.

[DawnLiExp]

Anyway, make sure to back up data or have a second boot drive. Happy coding!

[imothee]

@DawnLiExplorer what's strange is that RamDisk Manager could not mount the caches or temp file mounts on my system and there were no logs or errors, it just did nothing

Re. your issue, I'd suggest creating a folder like ~/Library/TmpCaches and then mounting TmpDisk to ~/Library/TmpCaches. Then if you set the symbolic link to be ~/Library/TmpCaches instead it will use the folder before the RamDisk is mounted so the system won't fail to boot. Since I couldn't get any logs or RamDisk Manager to work I am going to look at poking the decompiler to see if I can see anything but will continue my research.