How do I grant permission to edit a file on an SD card? [duplicate]

Is there a safe, stable application for reading from and writing to ext4 file systems on Mac OS X?

If not, what's the best way to access the contents of an ext4 file system on Mac OS X?

The answer depends on you willingness to invest in commercial software:

If you don’t mind spending some money on a commercial product, Paragon’s extFS for Mac will give you read and write access to ext2 / ext3 / ext4 file systems. The current version supports all versions of OS X / macOS from 10.10 upwards.

If you are looking for a free solution, you can setup a Linux virtual machine, mount your volume(s) there and share it / them via Samba or (S)FTP. This post has some details on how to achieve this using VirtualBox, a free virtual machine application. Note this is not exactly a lightweight solution, even if using a prebuilt VirtualBox VM will spare you installing and configuring a Linux distro from scratch.

Building on Ken's answer: I used fuse4x and fuse-ext2 successfully, and I recommend fuse-ext2 over ext4fuse. fuse-ext2 provides write access while ext4fuse provides only read access. Note that despite its name, fuse-ext2 supports EXT2/EXT3/EXT4.

ext4fuse was a hassle for me, because it requires manual compilation and has no support for fuse4x options that would allow me to set access control. fuse-ext2 provides downloadable packages, and the 0.0.7 version worked just fine. I copied a few large ISOs over without any problem.

One can also install OSXFUSE completely via the brew command line package manager:

brew install homebrew/fuse/ext4fuse

Note that the installation tells certain commands need to be run as 'sudo' in addition to this.

With Yosemite better have a look at this. And then make sure the directory is readable by your user by doing this. For it to work I had to use the wheel group like this:

sudo dscl . append /Groups/wheel GroupMembership $(whoami)