Linux file attributes(permissions)
lazarus / 62-General

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lagprogramming · 2015-08-15 15:06

I don't really understand the documentation. To set the
attributes(permissions) most probably I have to use BaseUnix.fpChmod.
The Execute attribute can be set for owner, group and others but to
read the attribute of the file I have to use BaseUnix.fpAccess.
fpAccess tests for the execute attribute but it does it only for "real
user ID". What's the equivalent of "real user ID" within owner, group
and others?
   I expect BaseUnix to be unavailable in windows. Within what ifdef
do I have to enclose BaseUnix when I put it an the uses?

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marcov · 2015-08-15 16:07

ifdef:  Unix

Both FPAccess and FPChMod are basically unix calls. Just look at their
man pages  (without the fp- prefix):

man 2  chmod

or

man 3 chmod

 (without 2 or 3 you get the manual page for the cmdline utility of
the same name)

chmod sets the _filesystems_ permissions, access checks the actual
permission

Real user id vs effective userid is mainly related to setuid
utilities. See e.g. http://www.lst.de/~okir/blackhats/node23.html

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Jonas Maebe · 2015-08-16 22:01

To read the permissions of a file, you generally use fpstat (man 2
stat). fpaccess is a shortcut for getting the permissions of the file,
your own effective user and possibly group id, checking whether this
combination allows you access, and in possibly checking any additional
file system specific access control mechanisms (e.g., OpenAFS even
completely ignores standard Unix permission flags and uses its own
access control lists instead).

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lagprogramming · 2015-08-29 14:32

Code: [Select]function CopyFileAttributes(const
sourcefile,destinationfile:string):boolean;
//Might require {$ifdef unix}baseunix{$endif} within uses
var fileinfo:{$ifdef unix}
             stat;
             {$endif}
             {$ifdef windows}
             longint;
             {$endif}
begin
if (fileexists(sourcefile) and fileexists(destinationfile)) then
   begin
   {$ifdef unix}
   exit((fpstat(sourcefile,fileinfo)=0)and(fpchmod(destinationfile,fil
einfo.st_mode)=0));
   {$endif}
   {$ifdef windows}
   fileinfo:=filegetattr(sourcefile);
   if fileinfo>=0 then exit(filesetattr(destinationfile,fileinfo)=0);
   {$endif}
   end;
result:=false;
end;

  If fpc's rtl already has such a function, you're welcome to reply
it's name. If not, I'm pretty sure that you might improve this one.
  In the future, I'd like a pair of cross platform functions like
FileGetAttr/FileSetAttr. The fact that the pair would use data that
makes sense only on the same file system, would not bother me.