chmod user:groups seems more portable, read bug #7602 and file #1462:

file changes
fix inconcistent use of chown user.group(linux) user:group (bsd) opt format

bin/sv_gpgcheckfiles: system("chown", "root:root", "-R", $cachedir);
bin/sv_update_conf: `chown root:$http_user $conffile_phpcopy $conffile` if $http_user;
# note "root.adm" typo ? may break if admin group doesn't exist
lib/perl5/Savane/Cvs.pm: system("chown", "root:admin", "$dir_cvs/CVSROOT", "-R");
lib/perl5/Savane/Download.pm: system('/bin/chown', "gatekpr:$name", $dir_public);
lib/perl5/Savane/Download.pm: system ('/bin/chown', 'upload:gatekpr', $dir_upload);
lib/perl5/Savane/Download.pm: system ('/bin/chown', 'gatekpr:gatekpr', $dir_ftpin);
lib/perl5/Savane/Download.pm: system ('/bin/chown', 'gatekpr:gatekpr', $dir_ftpout);