When booting Ubuntu (live session or for the first time) an 'ld-2.23.so' process consumes 100% CPU for minutes

[Daniel van Vugt]

When booting 20.04 (for the first time?) an 'ld-2.23.so' process consumes 100% CPU for minutes. It appears to be a child process of snapd.

This is happening consistently on multiple laptops.

[Daniel van Vugt (vanvugt)]

If this is really a necessary process then I suggest at least not running it in live sessions. It's seriously degrading to the user experience.

[Michael Vogt (mvo)]

I suspect this is the fontconfig cache generation, we run this during the install of a desktop snap. What does the live session seed? Maybe it can pre-generate the fontconfig caches during image build?

[Daniel van Vugt (vanvugt)]

I would not have thought that 'ld-2.23.so' was related to font caching. It's the dynamic linker/loader for shared libraries (man ld.so).

[Maciej Borzecki (maciek-borzecki)]

It is, the process is quite elaborate. Snapd runs fc-cache-* binary from the core snap by directly invoking ld.so (the interpreter) from the core snap, passing library path arguments that ensure that library dependencies come from core and lastly the binary itself. You can see it in action here: https://github.com/snapcore/snapd/blob/d4a45e9771e535da9bbe82be7c12e537d83e58cd/cmd/cmdutil/cmdutil.go#L100-L139

The side effect is that argv[0] is set to ld.so, so in ps output it looks like as if ld.so is running.

[Zygmunt Krynicki (zyga)]

Daniel, can you clarify two aspects please:

1) Were you booting a live CD or an installed system?
2) Were the machines reasonably fast or very old? Knowing the rough manufacture date, number of cores and amount of memory would help.

[Daniel van Vugt (vanvugt)]

1. Live USB
2. Reasonably fast i7-8500U (4 cores), 16GB RAM

[Daniel van Vugt (vanvugt)]

We don't necessarily need to redesign things and eliminate the process. If it's just given a very low priority so it doesn't impact the user experience then it wouldn't matter.

[Daniel van Vugt (vanvugt)]

Sorry comment #6 wasn't quite right. That machine is faster, but the problem still stands:

Asus Zenbook, i7-8550U (4 cores), 16GB RAM
snapd and its children hog one CPU core for 2 minutes
ld-2.23.so hogs a CPU core for less than 20 seconds

Microsoft Surface 3, x7-Z8700 (4 cores), 2GB RAM
snapd and its children hog one CPU core for 4 minutes
ld-2.23.so hogs a CPU core for a couple of minutes

[Daniel van Vugt (vanvugt)]

Again, using 100% CPU probably wouldn't matter if background tasks like snapd and its children had much lower priority.

[Daniel van Vugt (vanvugt)]

Fixed (?)

focal 20200124: This bug.
focal 20200220: No bug.

There were no QA-certified daily images between those two so I haven't dug any deeper to find out when the bug went away.

[Daniel van Vugt (vanvugt)]

The bug is back in the latest certified ISO:
http://cdimage.ubuntu.com/daily-live/20200309/

[Daniel van Vugt (vanvugt)]

On a (different) i7-8550U machine ld-2.23.so uses 100% CPU for about 18 seconds.

[Daniel van Vugt (vanvugt)]

Still happening in 20200401. The noisy laptop fan is a giveaway and 'top' confirms it's still this bug.

[Daniel van Vugt (vanvugt)]

Also observed on a fresh install of 18.04.3