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Ubuntu has been using [ext4 as the default since Ubuntu 9.10](https://wiki.ubuntu.com/KarmicKoala/TechnicalOverview#ext4_by_default) (2009), and the ext3 driver in the Linux kernel was [removed](https://lwn.net/Articles/651645/) in [version 4.3](https://kernelnewbies.org/Linux_4.3#The_Ext3_filesystem_has_been_removed) (2015), so internally, the ext4 driver has been mounting the ext3 images as loop devices for a long time already on Heroku runtime instances. All mounts that overlay the read-only root filesystem in containers, such as `/app`, have also been ext4 ever since it became the default: % heroku run -- mount | head Running mount on sushi... up, run.3567 /dev/loop17 on / type ext3 (ro,nosuid,nodev,nodiratime,relatime) none on /dev type tmpfs (rw,relatime,size=492k,mode=755,inode64) /dev/mapper/evg0-evol0 on /app type ext4 (rw,relatime) /dev/mapper/evg0-evol0 on /tmp type ext4 (rw,relatime) /dev/mapper/evg0-evol0 on /var/tmp type ext4 (rw,relatime) none on /proc type proc (rw,relatime) none on /dev type tmpfs (rw,nosuid,noatime,nodiratime,size=1024k,mode=755,inode64) none on /dev/shm type tmpfs (rw,nosuid,nodev,relatime,size=65536k,nr_inodes=2048,mode=700,uid=5790,gid=5790,inode64) /dev/mapper/evg0-evol0 on /etc/passwd type ext4 (ro,relatime) /dev/mapper/evg0-evol0 on /etc/group type ext4 (ro,relatime) GUS-W-21298571
edmorley
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dzuelke
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We started using on the `--platform` option of `docker image inspect` in #374, which is only available in Docker 28.1.0+: docker/cli#5934 GitHub recently reverted the changes announced in actions/runner-images#13474 as they were causing too many regressions for users, so the runners for now are back to Docker 28.0.4: actions/runner-images@8323333 Instead of relying on whatever Docker version the runners ship with, we now fetch the latest stable using `docker/setup-docker-action`, which will generally reduce our reliance on runner-images-induced regressions like this in the future. GUS-W-21410117
edmorley
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Mar 3, 2026
We started using on the `--platform` option of `docker image inspect` in #374, which is only available in Docker 28.1.0+: docker/cli#5934 GitHub recently reverted the changes announced in actions/runner-images#13474 as they were causing too many regressions for users, so the runners for now are back to Docker 28.0.4: actions/runner-images@8323333 Instead of relying on whatever Docker version the runners ship with, we now fetch the latest stable using `docker/setup-docker-action`, which will generally reduce our reliance on runner-images-induced regressions like this in the future. GUS-W-21410117
dzuelke
added a commit
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Mar 3, 2026
We started using on the `--platform` option of `docker image inspect` in #374, which is only available in Docker 28.1.0+: docker/cli#5934 GitHub recently reverted the changes announced in actions/runner-images#13474 as they were causing too many regressions for users, so the runners for now are back to Docker 28.0.4: actions/runner-images@8323333 Instead of relying on whatever Docker version the runners ship with, we now fetch the latest stable using `docker/setup-docker-action`, which will generally reduce our reliance on runner-images-induced regressions like this in the future. GUS-W-21410117
dzuelke
added a commit
that referenced
this pull request
Mar 3, 2026
We started using on the `--platform` option of `docker image inspect` in #374, which is only available in Docker 28.1.0+: docker/cli#5934 GitHub recently reverted the changes announced in actions/runner-images#13474 as they were causing too many regressions for users, so the runners for now are back to Docker 28.0.4: actions/runner-images@8323333 Instead of relying on whatever Docker version the runners ship with, we now fetch the latest stable using `docker/setup-docker-action`, which will generally reduce our reliance on runner-images-induced regressions like this in the future. GUS-W-21410117
dzuelke
added a commit
that referenced
this pull request
Mar 3, 2026
We started using on the `--platform` option of `docker image inspect` in #374, which is only available in Docker 28.1.0+: docker/cli#5934 GitHub recently reverted the changes announced in actions/runner-images#13474 as they were causing too many regressions for users, so the runners for now are back to Docker 28.0.4: actions/runner-images@8323333 Instead of relying on whatever Docker version the runners ship with, we now fetch the latest stable using `docker/setup-docker-action`, which will generally reduce our reliance on runner-images-induced regressions like this in the future. GUS-W-21410117
dzuelke
added a commit
that referenced
this pull request
Mar 3, 2026
We started using on the `--platform` option of `docker image inspect` in #374, which is only available in Docker 28.1.0+: docker/cli#5934 GitHub recently reverted the changes announced in actions/runner-images#13474 as they were causing too many regressions for users, so the runners for now are back to Docker 28.0.4: actions/runner-images@8323333 Instead of relying on whatever Docker version the runners ship with, we now fetch the latest stable using `docker/setup-docker-action`, which will generally reduce our reliance on runner-images-induced regressions like this in the future. GUS-W-21410117
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Ubuntu has been using ext4 as the default since Ubuntu 9.10 (2009), and the ext3 driver in the Linux kernel was removed in version 4.3 (2015), so internally, the ext4 driver has been mounting the ext3 images as loop devices for a long time already on Heroku runtime instances.
All mounts that overlay the read-only root filesystem in containers, such as
/app, have also been ext4 ever since it became the default:GUS-W-21298571