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Add an id for Docker containers #3

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merged 4 commits into from
Feb 1, 2023
Merged

Add an id for Docker containers #3

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14e376b
Add an id for Docker containers
juanbretti Jan 27, 2023
7b12ce3
Included "if 'docker' in mountinfo" for "linux"
juanbretti Jan 30, 2023
53a5807
Update __init__.py
juanbretti Jan 31, 2023
5ffae30
Update __init__.py
juanbretti Feb 1, 2023
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6 changes: 5 additions & 1 deletion machineid/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,11 @@ def id() -> str:
id = __read__('/var/lib/dbus/machine-id')
if not id:
id = __read__('/etc/machine-id')

if not id:
id = __exec__('head -1 /proc/self/cgroup|cut -d/ -f3')
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if not id:
id = __exec__("grep 'systemd' /proc/self/mountinfo|cut -d/ -f3")
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Suggested change
id = __exec__("grep 'systemd' /proc/self/mountinfo|cut -d/ -f3")
id = __exec__("grep 'systemd' /proc/self/mountinfo | cut -d/ -f3")

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Can you give me more detail on what /proc/self/mountinfo is and how it can be used as a unique ID? I don't think mountinfo is Docker-specific.

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@ezekg , this idea of using mountinfo, came from this post: https://stackoverflow.com/a/71823877/3780957
This post mentions, some versions do not have the ID at /proc/self/cgroup.
I am not sure if this is Docker specific. I can confirm that I check on a Docker instance, and that file has the same ID as /proc/self/cgroup.

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@ezekg ezekg Jan 30, 2023 •
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Got more info here. I think this is fine as long as you add a similar if 'docker' in mountinfo check as above.

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Also more discussion with the above workarounds is at opencontainers/runtime-spec#1105.

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Quick question, if __read__('/proc/self/mountinfo') returns None (because the file does not exist).
Will if 'docker' in mountinfo: return an exception?

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You’re right. I was only supplying pseudo code. I guess we should also check if mountinfo and 'docker' in mountinfo:. We shouldn’t raise an exception.

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You also need to fix the indentation (you're using 4 spaces but the rest of the file uses 2 spaces).

Please make sure the code runs.

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You’re right. I was only supplying pseudo code. I guess we should also check if mountinfo and 'docker' in mountinfo:. We shouldn’t raise an exception.

There is no additional exception.

Currently on a Docker container the if 'docker' in cgroup: does not find docker, the ending Exception works as intended. Same test with mountinfo.

When the full code does not find an ID raises the following:

Python 3.11.0 (main, Nov 15 2022, 19:58:01) [GCC 10.2.1 20210110] on linux                                                    
Type "help", "copyright", "credits" or "license" for more information.                                                        
>>> import machineid                                                                                                          
>>> print(machineid.id())                                                                                                     
Traceback (most recent call last):                                                                                            
  File "<stdin>", line 1, in <module>                                                                                         
  File "/usr/local/lib/python3.11/site-packages/machineid/__init__.py", line 90, in id                                        
    raise Exception('failed to obtain id on platform {}'.format(platform))                                                    
Exception: failed to obtain id on platform linux


if platform.startswith('openbsd') or platform.startswith('freebsd'):
id = __read__('/etc/hostid')
if not id:
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