Breaks bootloader if multiple menuentries present

[Vogtinator]

If there are multiple menuentry to be emitted into grub.cfg, the hack in /etc/grub.d/83_health_check_marker breaks, which results in a corrupted configuration file.

This can be fixed by replacing the ugly hack with a much nicer one:

 # Reopen the now changed output file in append mode
 exec >> "$cfgfile"

[Vogtinator]

Turns out the "much nicer hack" doesn't fully work either. I assumed that the scripts inside grub.d were sourced, but that's not the case, so they only share already opened file descriptors.

I'll try to find an equivalent of python3 -c 'import os; os.lseek(1, 0, os.SEEK_END)'.

[Vogtinator]

This seems to work fine:

dd oflag=append count=0 status=none

It does

[pid  1146] fcntl(1, F_GETFL)           = 0x8001 (flags O_WRONLY|O_LARGEFILE)
[pid  1146] fcntl(1, F_SETFL, O_WRONLY|O_APPEND|O_LARGEFILE) = 0

so forces the O_APPEND flag to stdout. This is not quite the same as seeking to the end of the replaced file content, but forces that every write to stdout ends up appended. That's arguably much better.

[laenion]

Using to dd to set O_APPEND now as suggested.