What does the '--' do in a normal syslinux config ? I used to see "quiet" after that , but don't know why.

Here's an example from Ubuntu 12.04:

label install
    menu label ^Install
    menu default
    kernel ubuntu-installer/amd64/linux
    append vga=788 initrd=ubuntu-installer/amd64/initrd.gz -- quiet 

Many commandline tools take arguments. There are one-letter, short, arguments and ... long arguments. They change the default behaviour of such a tool.

Short arguments are prefixed with a single dash - Long arguments are prefixed with a double dash --

Short arguments can be combined into ls -l -t -r is the same as ls -ltr. Long arguments need to be distinguished from combined singles, and to do that, a long argument is prefixed with a double dash ls -l -t --reverse or ls -lt --reverse

Long arguments are easier to remember, short ones faster to type.

Most commands have a manual page which explains these arguments in detail. Eg. man ls for the manual page of the ls command which I used in my examples above.

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  • 9
    I believe the original question is about the exact sequence -- in a configuration file, not the command line. GNU getopt(1) and getopt(3) use -- to signal the end of options. Everything after it is interpreted as an argument. E.g. grep -- -E file looks for the string -E in file (even though -E is a grep option). This could be what's happening here if syslinux (ab)uses getopt(3) to parse its configuration files. (or if it simulates the behaviour) – Alexios May 2 '12 at 15:28
  • @Alexios maybe you should put that as an answer – daisy May 10 '12 at 5:27
  • I would, but it's not really an answer. I know the conventional semantics of -- but I can't answer the question in spirit because I don't know what the heck it's doing in a SysLinux append line. :) – Alexios May 10 '12 at 9:23

Anything that is passed after the '--' are appended to the default options for the installed system. Everything before the '--' is only used by the installer itself.

Source: http://www.syslinux.org/archives/2009-December/013978.html

When the installation is finished you can find the options in the /etc/default/grub file at the line starting with GRUB_CMDLINE_LINUX_DEFAULT. If you edit this line you wille have to type update-grub so the content of this line is installed in the boot loader (used when launching the Linux kernel).

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  • 2
    +1 Though not nearly as verbose, this is the actual answer to the question being asked. – krowe Sep 6 '13 at 15:00
  • I added a few more infos. This answer now seems fine to me. – SamK Sep 7 '13 at 14:24

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