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#1 2015-10-05 06:35:07
- lilydjwg
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[SOLVED] How can I get current boot ID?
Well, I can get a list of boot IDs from journalctl --list-boots. But what to do if I want only the current one without reading all the journals?
Last edited by lilydjwg (2015-10-05 08:32:43)
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#2 2015-10-05 06:40:40
- jasonwryan
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Re: [SOLVED] How can I get current boot ID?
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#3 2015-10-05 07:56:19
- lilydjwg
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Re: [SOLVED] How can I get current boot ID?
I don't see any mention about boot IDs on that wiki page. Also I've checked some related manpages on journald and systemd but didn't see a light way to get the current boot ID.
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#4 2015-10-05 08:03:06
- jasonwryan
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Re: [SOLVED] How can I get current boot ID?
But what to do if I want only the current one without reading all the journals?
Show all messages from this boot:
# journalctl -b
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#5 2015-10-05 08:28:16
- Raynman
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Re: [SOLVED] How can I get current boot ID?
@jasonwryan: that's assuming OP wants to obtain the boot ID only to pass it to -b.
Well, I can get a list of boot IDs from journalctl --list-boots. But what to do if I want only the current one without reading all the journals?
This is a little confusing: you know how to get the boot IDs, why would you need to "read all the journals"? If you mean you have a long list of boots to scroll through, use `tail -1` or, for the ID without other fields:
$ journalctl --list-boots | awk 'END {print $2}'Offline
#6 2015-10-05 08:29:14
- lilydjwg
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Re: [SOLVED] How can I get current boot ID?
I mean the boot ID that systemd assgins to each boot, not the logs.
I can get the machine ID by `cat /etc/machine-id`, but I'm curious how to get the boot ID.
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#7 2015-10-05 08:32:14
- lilydjwg
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Re: [SOLVED] How can I get current boot ID?
OK, I've got it by reading the sources of journalctl. It's in /proc/sys/kernel/random/boot_id.
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#8 2015-10-05 09:01:07
- lilydjwg
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- Registered: 2010-06-20
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Re: [SOLVED] How can I get current boot ID?
@jasonwryan: that's assuming OP wants to obtain the boot ID only to pass it to -b.
This is a little confusing: you know how to get the boot IDs, why would you need to "read all the journals"? If you mean you have a long list of boots to scroll through, use `tail -1` or, for the ID without other fields:$ journalctl --list-boots | awk 'END {print $2}'
I presume journalctl will read the journals to find out what boot IDs it has. Anyway, it takes relatively a lot of time to get 128bit data that the system surely stores somewhere. I thought it's done by systemd, but it turns out the kernel generates it at /proc/sys/kernel/random/boot_id, and it's been there at least ten years ago!
I'm not going to pass it to journalctl. I see systemd has used it in private /tmp mount points and I may find a similar use in the future.
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