215 lines
7.1 KiB
Markdown
215 lines
7.1 KiB
Markdown
# Debugging Tips
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Sometimes things don't work the way they should. Here are some tips on debugging issues out
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in production.
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## Mail not working
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A common problem is that mails are not being sent for some reason. Suppose you configured
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an SMTP server, but you're not seeing mail delivered. Here's how to check the settings:
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1. Run a Rails console:
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```sh
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sudo gitlab-rails console production
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```
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or for source installs:
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```sh
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bundle exec rails console production
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```
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1. Look at the ActionMailer `delivery_method` to make sure it matches what you
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intended. If you configured SMTP, it should say `:smtp`. If you're using
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Sendmail, it should say `:sendmail`:
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```ruby
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irb(main):001:0> ActionMailer::Base.delivery_method
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=> :smtp
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```
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1. If you're using SMTP, check the mail settings:
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```ruby
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irb(main):002:0> ActionMailer::Base.smtp_settings
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=> {:address=>"localhost", :port=>25, :domain=>"localhost.localdomain", :user_name=>nil, :password=>nil, :authentication=>nil, :enable_starttls_auto=>true}```
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```
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In the example above, the SMTP server is configured for the local machine. If this is intended, you may need to check your local mail
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logs (e.g. `/var/log/mail.log`) for more details.
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1. Send a test message via the console.
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```ruby
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irb(main):003:0> Notify.test_email('youremail@email.com', 'Hello World', 'This is a test message').deliver_now
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```
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If you do not receive an e-mail and/or see an error message, then check
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your mail server settings.
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## Advanced Issues
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For more advanced issues, `gdb` is a must-have tool for debugging issues.
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### The GNU Project Debugger (gdb)
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To install on Ubuntu/Debian:
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```
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sudo apt-get install gdb
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```
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On CentOS:
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```
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sudo yum install gdb
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```
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### rbtrace
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GitLab 11.2 ships with [rbtrace](https://github.com/tmm1/rbtrace), which
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allows you to trace Ruby code, view all running threads, take memory dumps,
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and more. However, this is not enabled by default. To enable it, define the
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`ENABLE_RBTRACE` variable to the environment. For example, in Omnibus:
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```ruby
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gitlab_rails['env'] = {"ENABLE_RBTRACE" => "1"}
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```
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Then reconfigure the system and restart Unicorn and Sidekiq. To run this
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in Omnibus, run as root:
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```ruby
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/opt/gitlab/embedded/bin/ruby /opt/gitlab/embedded/bin/rbtrace
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```
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## Common Problems
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Many of the tips to diagnose issues below apply to many different situations. We'll use one
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concrete example to illustrate what you can do to learn what is going wrong.
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### 502 Gateway Timeout after unicorn spins at 100% CPU
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This error occurs when the Web server times out (default: 60 s) after not
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hearing back from the unicorn worker. If the CPU spins to 100% while this in
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progress, there may be something taking longer than it should.
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To fix this issue, we first need to figure out what is happening. The
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following tips are only recommended if you do NOT mind users being affected by
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downtime. Otherwise skip to the next section.
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1. Load the problematic URL
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1. Run `sudo gdb -p <PID>` to attach to the unicorn process.
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1. In the gdb window, type:
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```
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call (void) rb_backtrace()
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```
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1. This forces the process to generate a Ruby backtrace. Check
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`/var/log/gitlab/unicorn/unicorn_stderr.log` for the backtace. For example, you may see:
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```ruby
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:33:in `block in start'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:33:in `loop'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:36:in `block (2 levels) in start'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:44:in `sample'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:68:in `sample_objects'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:68:in `each_with_object'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:68:in `each'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:69:in `block in sample_objects'
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from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/sampler.rb:69:in `name'
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```
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1. To see the current threads, run:
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```
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thread apply all bt
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```
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1. Once you're done debugging with `gdb`, be sure to detach from the process and exit:
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```
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detach
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exit
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```
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Note that if the unicorn process terminates before you are able to run these
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commands, gdb will report an error. To buy more time, you can always raise the
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Unicorn timeout. For omnibus users, you can edit `/etc/gitlab/gitlab.rb` and
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increase it from 60 seconds to 300:
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```ruby
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unicorn['worker_timeout'] = 300
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```
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For source installations, edit `config/unicorn.rb`.
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[Reconfigure] GitLab for the changes to take effect.
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[Reconfigure]: ../restart_gitlab.md#omnibus-gitlab-reconfigure
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#### Troubleshooting without affecting other users
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The previous section attached to a running unicorn process, and this may have
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undesirable effects for users trying to access GitLab during this time. If you
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are concerned about affecting others during a production system, you can run a
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separate Rails process to debug the issue:
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1. Log in to your GitLab account.
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1. Copy the URL that is causing problems (e.g. https://gitlab.com/ABC).
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1. Create a Personal Access Token for your user (Profile Settings -> Access Tokens).
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1. Bring up the GitLab Rails console. For omnibus users, run:
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```
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sudo gitlab-rails console
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```
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1. At the Rails console, run:
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```ruby
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[1] pry(main)> app.get '<URL FROM STEP 2>/?private_token=<TOKEN FROM STEP 3>'
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```
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For example:
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```ruby
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[1] pry(main)> app.get 'https://gitlab.com/gitlab-org/gitlab-ce/issues/1?private_token=123456'
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```
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1. In a new window, run `top`. It should show this ruby process using 100% CPU. Write down the PID.
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1. Follow step 2 from the previous section on using gdb.
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### GitLab: API is not accessible
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This often occurs when gitlab-shell attempts to request authorization via the
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internal API (e.g., `http://localhost:8080/api/v4/internal/allowed`), and
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something in the check fails. There are many reasons why this may happen:
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1. Timeout connecting to a database (e.g., PostgreSQL or Redis)
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1. Error in Git hooks or push rules
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1. Error accessing the repository (e.g., stale NFS handles)
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To diagnose this problem, try to reproduce the problem and then see if there
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is a unicorn worker that is spinning via `top`. Try to use the `gdb`
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techniques above. In addition, using `strace` may help isolate issues:
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```shell
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strace -tt -T -f -s 1024 -p <PID of unicorn worker> -o /tmp/unicorn.txt
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```
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If you cannot isolate which Unicorn worker is the issue, try to run `strace`
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on all the Unicorn workers to see where the `/internal/allowed` endpoint gets
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stuck:
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```shell
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ps auwx | grep unicorn | awk '{ print " -p " $2}' | xargs strace -tt -T -f -s 1024 -o /tmp/unicorn.txt
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```
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The output in `/tmp/unicorn.txt` may help diagnose the root cause.
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# More information
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* [Debugging Stuck Ruby Processes](https://blog.newrelic.com/2013/04/29/debugging-stuck-ruby-processes-what-to-do-before-you-kill-9/)
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* [Cheatsheet of using gdb and ruby processes](gdb-stuck-ruby.txt)
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