046f987e02
See this doc: go/chromium-coil-change for more info
BUG=1210385
Change-Id: I6cd8548301e360bae8e71384dbd8ef11aa6c985f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2902904
Reviewed-by: My Nguyen <myy@chromium.org>
Commit-Queue: My Nguyen <myy@chromium.org>
Auto-Submit: John Palmer <jopalmer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#885851}
44 lines
2.0 KiB
Markdown
44 lines
2.0 KiB
Markdown
# Chrome Logging on Chrome OS
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## Locations
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Messages written via the logging macros in [base/logging.h] end up in different
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locations depending on Chrome's state:
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* `/var/log/ui/ui.LATEST` contains data written to stdout and stderr by Chrome
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(and technically also [session_manager]). This generally comprises messages
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that are written very early in Chrome's startup process, before logging has
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been initialized.
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* `/var/log/chrome/chrome` contains messages that are written before a user has
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logged in. It also contains messages written after login on test images, where
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chrome runs with `--disable-logging-redirect`.
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* `/home/chronos/user/log/chrome` contains messages that are written while a
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user is logged in on non-test images. Note that this path is within the user's
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encrypted home directory and is only accessible while the user is logged in.
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All of the above files are actually symlinks. Older log files can be found
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alongside them in the same directories.
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Also notable is `/var/log/messages`. This file contains general syslog messages,
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but it also includes messages written by `session_manager` that may be useful in
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determining when or why Chrome started or stopped.
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## Severity
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By default, only messages logged at severity `WARNING` or higher are written to
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disk. More concretely, `LOG(INFO)` messages are discarded.
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To enable `LOG(INFO)` message, pass `--log-level=0` to Chrome. See the
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[Passing Chrome flags from session_manager] document for more details, and
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specifically the `/etc/chrome_dev.conf` mechanism that can be used to
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change flags on development devices.
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## Verbose Logging
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When actively debugging issues, Chrome's `--vmodule` flag is sometimes used to
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temporarily log messages at lower severities for particular modules.
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[base/logging.h]: ../base/logging.h
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[session_manager]: https://chromium.googlesource.com/chromiumos/platform2/+/main/login_manager/
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[Passing Chrome flags from session_manager]: https://chromium.googlesource.com/chromiumos/platform2/+/main/login_manager/docs/flags.md
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