FTOOLS FITS Filename Filetypes
DESCRIPTION
The type of file specifies the medium on which the file is located
(eg, disk or network) and, hence, how to access the file. Currently
supported types are
file:// - file on local magnetic disk (default)
ftp:// - a readonly file accessed with the anonymous FTP protocol.
It also supports ftp://username:password@hostname/...
for accessing password-protected ftp sites.
http:// - a readonly file accessed with the HTTP protocol. It
does not support username:password like the ftp driver.
root:// - uses the CERN root protocol for writing as well as
reading files over the network.
shmem:// - opens or creates a file which persists in the computer's
shared memory.
mem:// - opens a temporary file in core memory. The file
disappears when the program exits so this is mainly
useful for test purposes when a permanent output file
is not desired.
If the filetype is not specified, then type file:// is assumed. The
double slashes '//' are optional and may be omitted in most cases.
Notes about the shmem filetype:
Shared memory files are currently supported on most Unix platforms,
where the shared memory segments are managed by the operating system
kernel and 'live' independently of processes. They are not deleted
(by default) when the process which created them terminates,
although they will disappear if the system is rebooted.
Applications can create shared memory files by specifying a filename
of the form 'shmem://h2' where the root `file' names are currently
restricted to be 'h0', 'h1', 'h2', 'h3', etc., up to a maximumn
number of 16. This is a preliminary implementation of the shared
memory interface. A more robust interface, which will have fewer
restrictions on the number of files and on their names, is planned
for the future.
This FITS file can then be opened by subsequent applications by
using the identical file name (e.g., 'shmem://h2'). Depending on
the application, the file may be opened with either READWRITE or
READONLY access just as with disk files. More than one process can
operate on READONLY mode files at the same time. Because
filelocking is supported (both in READONLY and READWRITE modes),
attempts to open the file may be locked out until another process
closes the file.
A shared memory management utility program called `smem', is
included with the CFITSIO distribution. It can be built by typing
`make smem'; then type `smem -h' to get a list of valid options.
Executing smem without any options causes it to list all the shared
memory segments currently residing in the system and managed by the
shared memory driver. To get a list of all the shared memory
objects, run the system utility program `ipcs [-a]'.
Notes about the root filetype
The original rootd server can be obtained from:
ftp://root.cern.ch/root/rootd.tar.gz
but, for it to work correctly with CFITSIO one has to use a modified
version which supports a command to return the length of the file.
This modified version is available in rootd subdirectory in the
CFITSIO ftp area at
ftp://legacy.gsfc.nasa.gov/software/fitsio/c/root/rootd.tar.gz.
This small server is started either by inetd when a client requests
a connection to a rootd server or by hand (i.e. from the command
line). The rootd server works with the ROOT TNetFile class. It
allows remote access to ROOT database files in either read or write
mode. By default TNetFile assumes port 432 (which requires rootd to
be started as root). To run rootd via inetd add the following line
to /etc/services: rootd 432/tcp and to /etc/inetd.conf, add the
following line:
rootd stream tcp nowait root /user/rdm/root/bin/rootd rootd -i
Force inetd to reread its conf file with "kill -HUP <pid inetd>".
You can also start rootd by hand running directly under your private
account (no root system priviliges needed). For example to start
rootd listening on port 5151 just type:
rootd -p 5151
Notice: no & is needed. Rootd will go into background by itself.
Rootd arguments:
-i says we were started by inetd
-p port# specifies a different port to listen on
-d level level of debug info written to syslog
0 = no debug (default)
1 = minimum
2 = medium
3 = maximum
Rootd can also be configured for anonymous usage (like anonymous
ftp). To setup rootd to accept anonymous logins do the following
(while being logged in as root):
- Add the following line to /etc/passwd:
rootd:*:71:72:Anonymous rootd:/var/spool/rootd:/bin/false
where you may modify the uid, gid (71, 72) and the home
directory to suite your system.
- Add the following line to /etc/group:
rootd:*:72:rootd
where the gid must match the gid in /etc/passwd.
- Create the directories:
mkdir /var/spool/rootd
mkdir /var/spool/rootd/tmp
chmod 777 /var/spool/rootd/tmp
Where /var/spool/rootd must match the rootd home directory as
specified in the rootd /etc/passwd entry.
- To make writeable directories for anonymous do, for example:
mkdir /var/spool/rootd/pub
chown rootd:rootd /var/spool/rootd/pub
That's all. Several additional remarks: you can login to an
anonymous server either with the names "anonymous" or "rootd". The
password should be of type user@host.do.main. Only the @ is enforced
for the time being. In anonymous mode the top of the file tree is
set to the rootd home directory, therefore only files below the home
directory can be accessed. Anonymous mode only works when the
server is started via inetd.
SEE ALSO
filenames