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Wicked PDF does not render documents itself: it starts the external wkhtmltopdf executable. A working Rails gem therefore requires four things at runtime: the gem must be in the deployed Bundler environment, Wicked PDF must resolve the correct executable, the process must be able to execute and (for wkhtmltopdf-binary) unpack it, and the operating system must provide compatible libraries, fonts and temporary storage. Check those in that order before changing view options.
What the error actually means
Wicked PDF is a Rails wrapper around the shell utility wkhtmltopdf. Rails can load the wicked_pdf gem while the command is absent, inaccessible or unable to start. Messages such as PDF could not be generated, cannot find wkhtmltopdf and exit status 127 are symptoms of different failures, so identify the failing layer first.
| Symptom | Most likely layer | First check |
|---|---|---|
Bundler says wkhtmltopdf-binary is not included |
Deployment bundle | Loaded gem path in the same release and process context |
| Wicked PDF cannot find the executable | Path resolution | Wicked’s resolved path and exe_path |
Exit 127; loader reports missing libssl.so.1.1 or libcrypto.so.1.1 |
OS ABI/runtime | Binary, libc and OpenSSL compatibility |
| Executable starts but images or CSS are missing | HTML assets | Absolute URLs, helpers, network access and fonts |
| Intermittent tempfile or extraction errors | Filesystem permissions | TMPDIR, gem-directory write access and disk space |
1. Verify the deployed bundle, not your development machine
Run this from the release directory, with the same Ruby, Bundler configuration and service account that runs Rails:
bundle exec ruby -e 'puts Gem.loaded_specs["wkhtmltopdf-binary"]&.&.full_gem_path'A printed directory confirms that Bundler activated the gem. A blank result means the process cannot load it, even if /bin/wkhtmltopdf exists. Check the production Gemfile and lockfile, then deploy the updated bundle. Do not rely on an interactive shell’s gems or PATH: systemd, containers, job workers and application servers often have different environments.
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- Put
gem 'wkhtmltopdf-binary'in a bundle group that is installed in production. - Run
bundle checkandbundle execunder the service user. - Restart the Rails process after changing gems or environment variables.
PATH visibility and Bundler activation are separate checks. You need both when the application is configured to discover a command rather than use an explicit path.
2. See and set the path Wicked PDF uses
In a Rails console opened in the deployed environment, inspect Wicked PDF’s resolver:
WickedPdf.new.send(:find_wkhtmltopdf_binary_path)If it returns a nonexistent location, configure the actual executable in an initializer (for example, config/initializers/wicked_pdf.rb):
WickedPdf.configure do |c|
c.exe_path = '/usr/local/bin/wkhtmltopdf'
c.enable_local_file_access = true
endUse the path that exists in the running image or host, not the path from a build stage. If you want the binary gem’s extracted executable, inspect its gem directory and set exe_path only after confirming the file is present and executable. Keep this configuration in source control so CI, staging and production use the same rule.
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wkhtmltopdf-binary ships compressed platform binaries. On first use it selects a match and extracts the executable into the gem directory. The Rails process therefore needs write permission there until extraction completes, as well as execute permission afterward.
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- Identify the gem directory with the Bundler command above.
- As the application user, verify that directory is writable and that the extracted file can be executed.
- Warm the binary during deployment or a health check, before putting traffic on a new release.
- After extraction, remove unnecessary write access if your deployment policy requires an immutable filesystem; retain execute and read access.
Read-only container layers commonly fail on this first run. Extract during the image build into a writable persistent layer, or use a distribution package and explicit exe_path instead. Avoid “fixes” that make the entire filesystem writable when only the gem directory or a cache volume is needed.
4. Diagnose exit 127 before changing Wicked PDF options
Exit 127 generally means the command could not be started or its dynamic loader could not load a required library. On Alpine, a reported 0.12.5 binary failed after an OpenSSL 3 upgrade because libssl.so.1.1 and libcrypto.so.1.1 were missing. This is an operating-system compatibility failure; HTML flags, JavaScript delays and Rails view code cannot repair it.
Choose a compatible binary and base image
- Match the binary’s libc and OpenSSL ABI to the image that runs Rails.
- Use a supported distribution package when the binary gem does not match your platform.
- Pin the base image and package versions so a routine OpenSSL or libc upgrade does not silently change the loader environment.
- Test the exact production image, not only a development laptop.
On minimal Alpine-style images, verify whether the downloaded executable expects glibc while the image supplies musl. Installing a random compatibility package may mask one missing library and leave the binary unsupported; replacing it with a binary built for the image is usually more reliable.
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command -v wkhtmltopdf
ls -l /actual/path/wkhtmltopdf
/actual/path/wkhtmltopdf --version
ldd /actual/path/wkhtmltopdfcommand -v tests PATH, --version tests startup, and ldd exposes unresolved shared libraries on systems that provide it. If --version fails, stop there and repair the image or binary before investigating HTML.
5. Check temporary directories and permissions
Wicked PDF and the executable create temporary files. A valid path can still fail when TMPDIR points to a nonexistent directory, the directory is not writable, disk space is exhausted or a container mounts it with restrictive permissions.
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- Print the runtime value of
ENV['TMPDIR']from the Rails process. - Confirm the directory exists, is writable by the service account and has sufficient space.
- Reproduce a conversion under that account, not as root.
- Check cleanup behavior and inode limits when many PDFs are generated concurrently.
Use a dedicated writable temporary volume in containers and set TMPDIR explicitly when the platform’s default is unsuitable. Never put secrets in generated temporary paths or log complete URLs containing credentials.
6. Supply fonts and rendering dependencies
Even after the executable starts, output can be blank, clipped or visually different when the image lacks the fonts and libraries used by the document. The wkhtmltopdf runtime depends on fontconfig and freetype2. Install the fonts your PDFs actually require, then refresh or point fontconfig at them (for example with FONTCONFIG_PATH in a custom image).
- Include Latin, CJK, emoji or corporate fonts explicitly when documents use them.
- Rebuild the font cache during image creation where your distribution requires it.
- Compare a known test page in CI so a base-image change is visible.
Font problems are rendering problems, not executable-discovery problems: do not “solve” them by adding more PATH entries.
7. Make CSS, JavaScript and images reachable
wkhtmltopdf runs outside the Rails request process. Relative asset paths that work in a browser can fail when the converter has no matching current URL, authentication cookie or host resolution. Use absolute, reachable URLs or Wicked PDF’s asset helpers (such as the wicked_pdf_* helpers) in the HTML you render.
- Ensure the converter can resolve the hostname from its network namespace.
- Provide authentication headers or a signed asset URL when assets are protected.
- Use the local-file option only when you intentionally serve local assets; keep
enable_local_file_accessscoped to the files required. - Check every image and stylesheet. A missing image can affect other images in the same document, so fix the first failed asset rather than accepting a partially rendered PDF.
For JavaScript-heavy pages, wait for the content your template needs and make sure external scripts are available from the converter’s network. A successful process exit does not guarantee that dynamic content finished rendering.
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8. A repeatable production repair sequence
- Run the Bundler gem-path command in the deployed context.
- Inspect
find_wkhtmltopdf_binary_pathand compare it with the file inside the running host or container. - Set
c.exe_pathexplicitly when discovery is unreliable. - Allow first-run extraction, then verify execute permission.
- Run
wkhtmltopdf --versionand inspect loader dependencies; repair libc/OpenSSL mismatches. - Verify
TMPDIR, disk space and tempfile permissions. - Install and configure required fonts.
- Render a minimal HTML page, then add CSS, images and JavaScript one dependency at a time.
- Pin the resulting image, gem lockfile and initializer in CI and production.
How to compare repair options
| Repair choice | Advantages | Risks to verify |
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| Binary gem with explicit path | Simple Bundler deployment and repeatable Rails configuration | Extraction permissions and platform/ABI support |
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Evaluate each candidate on binary provenance and version, OS/libc/OpenSSL compatibility, execution and unpack permissions, temporary storage, fonts and assets, and whether CI can reproduce production exactly.
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Troubleshooting checklist by error
“cannot find wkhtmltopdf”
Confirm the gem is activated, inspect Wicked’s resolved path, then set exe_path to an executable file in the running environment. Restart Rails after changing the initializer.
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“PDF could not be generated” with no loader message
Run the executable directly as the service user, then test a minimal page. If direct startup works, inspect temporary storage and asset URLs; if it does not, repair the binary/runtime first.
Exit 127 after an image or OpenSSL update
Look for missing shared libraries such as libssl.so.1.1 or libcrypto.so.1.1. Pin a compatible image/package or replace the binary; Wicked PDF options are unrelated.
First request fails, later requests work
The binary likely could not unpack on first use. Grant temporary gem-directory write access or extract during deployment, then verify the extracted file’s permissions.
PDF opens but is missing images or fonts
Use absolute or Wicked PDF helper URLs, verify network and authentication, install the required fonts and check fontconfig. Test assets individually.
FAQ
Should I install both a system package and wkhtmltopdf-binary?
Usually choose one controlled source and configure it explicitly. Installing both can hide which executable Rails actually invokes and makes upgrades harder to reproduce.
Can changing enable_local_file_access fix exit 127?
No. That option affects access to local assets after the process starts. Exit 127 indicates command startup or loader failure.
Why does it work in a Rails console but fail in a job worker?
The worker may use a different service account, environment, container image, PATH, TMPDIR or Bundler group. Compare those values in the failing process rather than the interactive console.
Do I need a compatibility matrix for every Ruby and Rails version?
No universal matrix covers every combination. Pin and test the binary, base image, libc/OpenSSL libraries, fonts and deployment process that you actually ship.
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