[aur-general] Why /etc/issue starts with invisible chars?

[Roman Kyrylych]

2008/3/21, Lyman <lymanrb at gmail.com>:
> Roman Kyrylych 写道:
>
> > 2008/3/21, Lyman <lymanrb at gmail.com>:
>  >> Hi, all
>  >>
>  >>  I found this issue when I was trying Sysmonitor in the package
>  >>  screenlets because Sysmonitor can not show my distribution name correctly.
>  >>
>  >>  At the beginning I thought that it was a bug of screenlets, however,
>  >>  when I dug into its source code, I realized that it could be a "bug"
>  >>  introduced by Archlinux because the /etc/issue starts with some
>  >>  invisible chars.
>  >>
>  >>  Here's the hexdump of /etc/issue in Archlinux. It is obviously that the
>  >>  first line in this file is not the distribution name.
>  >>
>  >>  00000000  1b 5b 48 1b 5b 32 4a 0a  41 72 63 68 20 4c 69 6e
>  >>  |.[H.[2J.Arch Lin|
>  >>  00000010  75 78 20 28 43 6f 72 65  20 44 75 6d 70 29 20 20  |ux (Core
>  >>  Dump)  |
>  >>  00000020  5c 72 20 20 28 5c 6e 29  20 28 5c 6c 29 0a 0a     |\r  (\n)
>  >>  (\l)..|
>  >>
>  >>  I've checked other two distribution, CentOS and Ubuntu (that's all I
>  >>  have at the moment), both of them presents the their name in the first line.
>  >>
>  >>  I guess most of the applications just use the first line in /etc/issue
>  >>  as distribution name (so do screenlets). I think Archlinux should comply
>  >>  with "Rule of Least Surprise" on this issue. If the invisible chars are
>  >>  just for clearing screen, we can do that from the second line.
>  >
>  > We already do. :-)
>  > /etc/issue is *not* a way to check for distribution name. Apps that do
>  > this are wrong.
>  > Most distros have /etc/distroname-release files as well (that contain
>  > the version, that's why it's empty in Arch).
>
> Things seem not that simple, though. On CentOS, I found
>  /etc/redhat-release. On Ubuntu, there's no /etc/ubuntu-release but only
>  /etc/lsb-release. Unfortunately, the latter one is a formatted text file
>  and applications can not depend on it by a rule as simple as "the first
>  line".

/etc/lsb-release is defined in LSB, maybe there are simpler ways to
get distro name on LSB compliant system, I don't know.

>
>  Considering there's so many distributions in Linux world, it seems quite
>  confusing for developers to do something absolutely "correct", right?
>
>  I will forward these information to the developers of screenlets.
>  However, I still insisted on suggesting changing /etc/issue to a
>  "normal" one because I didn't see any advantages of inserting invisible
>  chars in the first line. By doing just a little "favor", it will makes
>  Archlinux more "compatible" && friendly to both developers and end
>  users, I think.

Ok, I'll explain it in another way: /etc/issue is intended to be
customized by user,
thus software should *not* rely on it to get a distro name.
/etc/distroname-release was invented exactly to solve this issue.

If developers of screenlets wanted to make their life easier by
writing less lines of code and relying on /etc/issue to have a
distroname as first word/line - that's clearly a bug (or let's say
"wrong solution") in their code.

We will not "fix" it by changing our /etc/issue.
BTW, removing those "invisible" chars at the beginning makes the text
appear on screen without cleaning it first, so you'll see the rest of
daemons loading output.

>  > Good written apps check for *existence* of /etc/arch-release file to
>  > know whether they are on Arch Linux.
>  > See virtualbox's installer for example how a check for distribution
>  > should be made.
>  >
>
> Can you please point out which file is the installer? There's so many
>  files in the package virtualbox-ose and I failed to find an "obvious"
>  installer. Thanks.

See http://virtualbox.org/browser/trunk/src/VBox/Installer/linux/VBoxSysInfo.sh
Notice that all distros except Ubuntu use /etc/distroname-release even
those that are LSB-compliant (I believe at least Fedora is).

-- 
Roman Kyrylych (Роман Кирилич)