[Bug] Linux cache seems to be broken

[eduardbosch-jt]

• I have gone through the action README, documentation and wiki.
• I don't see my issue listed in existing issues.

Describe the bug
When I enable the cache in Linux, it fails to recover the swift installation.

To Reproduce

1. I'm using a self-hosted runners, but I guess that issue should be on any runner.
2. Run a workflow installing Swift with cache enabled (default)
3. Wait for it to finish and ensure the cache has been created.
4. Run the workflow again.

Expected behavior
The Swift should be restored from cache successfully.

Logs

/home/runner/_work/_tool/swift-6.3.2-RELEASE-ubuntu2404/6.3.2/x86_64/usr/bin/swift --version
/home/runner/_work/_tool/swift-6.3.2-RELEASE-ubuntu2404/6.3.2/x86_64/usr/bin/swift: error while loading shared libraries: libncurses.so.6: cannot open shared object file: No such file or directory
Error: The process '/home/runner/_work/_tool/swift-6.3.2-RELEASE-ubuntu2404/6.3.2/x86_64/usr/bin/swift' failed with exit code 127

Screenshots
If applicable, add screenshots to help explain your problem.

Runner (please complete the following information):

• Name: Detected linux platform "Ubuntu" version "24.04" with arch "x64"
• OS: Linux
• Version 24.04

[soumyamahunt]

@eduardbosch-jt can you share the complete logs?

[eduardbosch-jt]

There's not much more than that, but here's the full log:

1m 46s
Run SwiftyLab/setup-swift@38f54a76b70d989321de9dc7c840618c08cf56e9
  with:
    swift-version: 6.3.2
    development: false
    check-latest: false
    dry-run: false
    cache-snapshot: true
    prefer-oss-toolchain: false
    prefer-visual-studio-linker: false
    update-sdk-modules: false
  env:
    OTEL_EXPORTER_OTLP_ENDPOINT: …
Syncing swift.org data
  /usr/bin/git init /home/runner/_work/_actions/SwiftyLab/setup-swift/38f54a76b70d989321de9dc7c840618c08cf56e9/swiftorg
  hint: Using 'master' as the name for the initial branch. This default branch name
  hint: will change to "main" in Git 3.0. To configure the initial branch name
  hint: to use in all of your new repositories, which will suppress this warning,
  hint: call:
  hint:
  hint: 	git config --global init.defaultBranch <name>
  hint:
  hint: Names commonly chosen instead of 'master' are 'main', 'trunk' and
  hint: 'development'. The just-created branch can be renamed via this command:
  hint:
  hint: 	git branch -m <name>
  hint:
  hint: Disable this message with "git config set advice.defaultBranchName false"
  Initialized empty Git repository in /home/runner/_work/_actions/SwiftyLab/setup-swift/38f54a76b70d989321de9dc7c840618c08cf56e9/swiftorg/.git/
  /usr/bin/git fetch https://github.com/apple/swift-org-website.git 243bea7659ab710ee435832117f6b8a6f4532d7d --depth=1 --no-tags
  From https://github.com/apple/swift-org-website
   * branch            243bea7659ab710ee435832117f6b8a6f4532d7d -> FETCH_HEAD
  /usr/bin/git checkout FETCH_HEAD --detach
  HEAD is now at 243bea7 Add Nightly swift-6.4.x-DEVELOPMENT-SNAPSHOT-2026-05-31-a
Detecting current platform
  Detected linux platform "Ubuntu" version "24.04" with arch "x64"
Installing Swift toolchain snapshot swift-6.3.2-RELEASE
  No SDKs to install
  Cache hit for: swift-6.3.2-RELEASE-ubuntu2404-x86_64
  Received 0 of 972183130 (0.0%), 0.0 MBs/sec
  Received 88080384 of 972183130 (9.1%), 42.0 MBs/sec
  Received 167772160 of 972183130 (17.3%), 53.3 MBs/sec
  Received 260046848 of 972183130 (26.7%), 61.9 MBs/sec
  Received 297795584 of 972183130 (30.6%), 56.7 MBs/sec
  Received 385875968 of 972183130 (39.7%), 61.3 MBs/sec
  Received 465567744 of 972183130 (47.9%), 63.4 MBs/sec
  Received 536870912 of 972183130 (55.2%), 64.0 MBs/sec
  Received 608174080 of 972183130 (62.6%), 64.4 MBs/sec
  Received 671088640 of 972183130 (69.0%), 64.0 MBs/sec
  Received 746586112 of 972183130 (76.8%), 64.7 MBs/sec
  Received 805306368 of 972183130 (82.8%), 64.0 MBs/sec
  Received 872415232 of 972183130 (89.7%), 64.0 MBs/sec
  Received 939524096 of 972183130 (96.6%), 64.0 MBs/sec
  Received 972183130 of 972183130 (100.0%), 64.1 MBs/sec
  Cache Size: ~927 MB (972183130 B)
  /usr/bin/tar -xf /home/runner/_work/_temp/74dc70d8-b3ba-48e9-b6ce-b32746971b0a/cache.tzst -P -C /home/runner/_work/ios-companies/ios-companies --use-compress-program unzstd
  Cache restored successfully
/home/runner/_work/_tool/swift-6.3.2-RELEASE-ubuntu2404/6.3.2/x86_64/usr/bin/swift --version
/home/runner/_work/_tool/swift-6.3.2-RELEASE-ubuntu2404/6.3.2/x86_64/usr/bin/swift: error while loading shared libraries: libncurses.so.6: cannot open shared object file: No such file or directory
Error: The process '/home/runner/_work/_tool/swift-6.3.2-RELEASE-ubuntu2404/6.3.2/x86_64/usr/bin/swift' failed with exit code 127

[soumyamahunt]

@eduardbosch-jt the library libncurses.so doesn't seem to be part of Swift installation, hence the issue can't be related to caching. This library is a system component in Ubuntu GitHub runners.

Are you facing this issue in self-hosted runners? Can you provide output for following script when executed as part of your job (execute as a step before the setup swift step) in the event of such error:

echo "libncurses location:"
ldconfig -p | grep libncurses
echo "ld conf:"
cat /etc/ld.so.conf
echo "ld custom conf:"
cat /etc/ld.so.conf.d/*.conf
echo "ld lib path:"
echo $LD_LIBRARY_PATH

For example, I don't face this error with default runners and get output for ubuntu-latest runner:

libncurses location:
libncursesw.so.6 (libc6,x86-64) => /lib/x86_64-linux-gnu/libncursesw.so.6
libncurses.so.6 (libc6,x86-64) => /lib/x86_64-linux-gnu/libncurses.so.6
ld conf:
include /etc/ld.so.conf.d/*.conf

ld custom conf:
/usr/lib/x86_64-linux-gnu/libfakeroot

libc default configuration

/usr/local/lib

Multiarch support

/usr/local/lib/x86_64-linux-gnu
/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu

Legacy biarch compatibility support

/lib32
/usr/lib32
ld lib path:

[eduardbosch-jt]

Hey @soumyamahunt
I've tested it and as you can see, libncurses.so is missing only when the cache is enabled:

Cache disabled	Cache enabled

Probably the issue is that we are not installing dependencies when we restore the cache, but only on the first install. WDYT about installing dependencies in unpack also?
Check the install dependencies when downloading Swift:

setup-swift/src/installer/linux.ts

Line 48 in 9c91a6b

this.installDependencies(),

[soumyamahunt]

The missing dependencies install could be a cause. Thanks @eduardbosch-jt for pointing it out. I have created a fix with #518. Can you try using the branch linux-deps-setup and see if it fixes your issue?