hlfsd - home-link file system daemon
hlfsd [ -fhnpvC ] [ -a alt_dir ] [ -c cache-interval ] [ -g group ] [ -i reload-interval ]
[ -l logfile ] [ -o mount-options ] [ -x log-options ] [ -D debug-options ] [ -P password-
file ] [ linkname [ subdir ] ]
Hlfsd is a daemon which implements a filesystem containing a symbolic link to subdirectory
within a user's home directory, depending on the user which accessed that link. It was
primarily designed to redirect incoming mail to users' home directories, so that it can
read from anywhere.
Hlfsd operates by mounting itself as an NFS server for the directory containing linkname,
which defaults to /hlfs/home. Lookups within that directory are handled by hlfsd, which
uses the password map to determine how to resolve the lookup. The directory will be cre-
ated if it doesn't already exist. The symbolic link will be to the accessing user's home
directory, with subdir appended to it. If not specified, subdir defaults to .hlfsdir.
This directory will also be created if it does not already exist.
A SIGTERM sent to hlfsd will cause it to shutdown. A SIGHUP will flush the internal
caches, and reload the password map. It will also close and reopen the log file, to
enable the original log file to be removed or rotated. A SIGUSR1 will cause it to dump
its internal table of user IDs and home directories to the file
Alternate directory. The name of the directory to which the symbolic link returned
by hlfsd will point, if it cannot access the home directory of the user. This
defaults to /var/hlfs. This directory will be created if it doesn't exist. It is
expected that either users will read these files, or the system administrators will
run a script to resend this "lost mail" to its owner.
Caching interval. Hlfsd will cache the validity of home directories for this
interval, in seconds. Entries which have been verified within the last cache-
interval seconds will not be verified again, since the operation could be expen-
sive, and the entries are most likely still valid. After the interval has expired,
hlfsd will re-verify the validity of the user's home directory, and reset the cache
time-counter. The default value for cache-interval is 300 seconds (5 minutes).
-f Force fast startup. This option tells hlfsd to skip startup-time consistency
checks such as existence of mount directory, alternate spool directory, symlink to
be hidden under the mount directory, their permissions and validity.
Set the special group HLFS_GID to group. Programs such as from or comsat, which
access the mailboxes of other users) must be setgid HLFS_GID to work properly. The
default group is "hlfs". If no group is provided, and there is no group "hlfs",
this feature is disabled.
-h Help. Print a brief help message, and exit.
Map-reloading interval. Each reload-interval seconds, hlfsd will reload the pass-
word map. Hlfsd needs the password map for the UIDs and home directory pathnames.
Hlfsd schedules a SIGALRM to reload the password maps. A SIGHUP sent to hlfsd will
force it to reload the maps immediately. The default value for reload-interval is
900 seconds (15 minutes.)
Specify a log file to which hlfsd will record events. If logfile is the string
syslog then the log messages will be sent to the system log daemon by syslog(3),
using the LOG_DAEMON facility. This is also the default.
-n No verify. Hlfsd will not verify the validity of the symbolic link it will be
returning, or that the user's home directory contains sufficient disk-space for
spooling. This can speed up hlfsd at the cost of possibly returning symbolic links
to home directories which are not currently accessible or are full. By default,
hlfsd validates the symbolic-link in the background. The -n option overrides the
meaning of the -c option, since no caching is necessary.
Mount options. Mount options which hlfsd will use to mount itself on top of
dirname. By default, mount-options is set to "ro". If the system supports sym-
bolic-link caching, default options are set to "ro,nocache".
-p Print PID. Outputs the process-id of hlfsd to standard output where it can be
saved into a file.
-v Version. Displays version information to standard error.
Specify run-time logging options. The options are a comma separated list chosen
from: fatal, error, user, warn, info, map, stats, all.
-C Force hlfsd to run on systems that cannot turn off the NFS attribute-cache. Use of
this option on those systems is discouraged, as it may result in loss or misdeliv-
ery of mail. The option is ignored on systems that can turn off the attribute-
Select from a variety of debugging options. Prefixing an option with the string no
reverses the effect of that option. Options are cumulative. The most useful
option is all. Since this option is only used for debugging other options are not
documented here. A fuller description is available in the program source. A
SIGUSR1 sent to hlfsd will cause it to dump its internal password map to the file
Read the user-name, user-id, and home directory information from the file password-
file. Normally, hlfsd will use getpwent(3) to read the password database. This
option allows you to override the default database, and is useful if you want to
map users' mail files to a directory other than their home directory. Only the
username, uid, and home-directory fields of the file password-file are read and
checked. All other fields are ignored. The file password-file must otherwise be
compliant with Unix System 7 colon-delimited format passwd(4).
directory under which hlfsd mounts itself and manages the symbolic link home.
default sub-directory in the user's home directory, to which the home symbolic link
returned by hlfsd points.
directory to which home symbolic link returned by hlfsd points if it is unable to
verify the that user's home directory is accessible.
amd(8), automount(8), cron(8), getgrent(3), getpwent(3), mail(1), mnttab(4), mount(8),
mtab(5), passwd(4), sendmail(8), umount(8).
HLFSD: Delivering Email to Your $HOME, in Proc. LISA-VII, The 7th Usenix System Adminis-
tration Conference, November 1993.
Erez Zadok <firstname.lastname@example.org>, Computer Science Department, Columbia University, New
York City, New York, USA, and Alexander Dupuy <email@example.com>, System Management ARTS,
White Plains, New York, USA.
14 September 1993 HLFSD(8)