Named pipes in the server z/OS UNIX file system

When files are stored in the server z/OS® UNIX file system as named pipes, you can delete, rename, and list the named pipes using these z/OS FTP subcommands:

DELEte
DIr
LS
MDelete
REName

With other FTP clients, you can specify a named pipe as the argument of these commands: DELE, RNFR, RNTO, LIST, NLST.

Using the z/OS FTP client, you can create a named pipe in the server z/OS UNIX file system with this subcommand:

MKFifo

From other FTP clients, you can use the QUOTE subcommand to send an XFIF command to the remote host:

QUOTE XFIF <pathname>

When you configure UNIXFILETYPE FIFO at the FTP server, all files you send to the server z/OS UNIX file system are stored as named pipes, and you can retrieve data from named pipes in the server z/OS UNIX file system.

You can use these z/OS FTP subcommands to retrieve from named pipes in the FTP server file system:

Get
MGet

From other FTP clients, use the RETR command to retrieve data from named pipes.

The FTP server can retrieve data only from existing named pipes. You can create the named pipe as described earlier in this section, or another process on the FTP server host can create the named pipe.

You can use these z/OS FTP subcommands to send files to named pipes in the server z/OS UNIX file system:

APpend
Put
MPut

Use the SUnique subcommand to set store-unique off before using the Put or MPut subcommand to send files to named pipes.

From other FTP clients, you can use APPE or STOR commands to store a file as a named pipe in the server file system.

Unlike most types of z/OS UNIX files, data written to a named pipe is always appended to existing data rather than replacing existing data. Therefore, the STOR command is equivalent to the APPE command when UNIXFILETYPE=FIFO is configured. You cannot replace a named pipe by issuing the STOR command as you can with other types of files in the z/OS UNIX file system.

Unlike most types of z/OS UNIX files, data read from a named pipe is removed from the named pipe permanently. Retrieving data from a named pipe in the server file system destroys the contents of the named pipe.

Restrictions:

Anonymous users are not allowed to read from or write to named pipes in the z/OS FTP server z/OS UNIX file system.
The STOU (Store-unique) command is not allowed when UNIXFILETYPE=FIFO is configured.
The z/OS operating system does not provide serialization for named pipes. Multiple processes on the server can read from or write to the same named pipe concurrently.
Restart of file transfers to or from named pipes is not allowed.

Results: The following results apply when the server stores a file as a named pipe in the z/OS UNIX file system:

The server waits up to the number of seconds specified by the FIFOOPENTIME configuration option to open the named pipe for writing. The FTP server cannot open the named pipe until the process that reads from the named pipe opens the pipe. A large FIFOOPENTIME value gives you more time to start the named pipe reader, but could cause the data connection to time out if the server waits for the number of seconds specified by the FIFOOPENTIME value.
If you issue the MPut subcommand, the server blocks for the number of seconds specified by the FIFOOPENTIME value for each remote named pipe that is not opened for reading by a process on the FTP server host at the time of transfer.
The server waits up to the number of seconds specified by the FIFOIOTIME value for each write to the named pipe to complete. In general, the server does not block during writes unless it writes to the named pipe much faster than the named pipe reader reads from the pipe. If the server does not write any data to the named pipe for the number of seconds specified by the FIFOIOTIME value, it fails the file transfer.

The following results apply when the server retrieves data from a named pipe in the z/OS UNIX file system:

The server waits up to the number of seconds specified by the FIFOOPENTIME value to open the named pipe for reading. The FTP server cannot open the named pipe until the process that writes to the named pipe opens the pipe. A large FIFOOPENTIME value gives you more time to start the named pipe writer, but could cause the data connection to time out if the server waits for the number of seconds specified by the FIFOOPENTIME value.
If you issue the MGet subcommand, the server blocks for the number of seconds specified by the FIFOOPENTIME value for each remote named pipe that is not opened for writing by a process on the FTP server host at the time of transfer.
The server waits up to the number of seconds specified by the FIFOIOTIME value for each read from the named pipe to complete. The server might block if the pipe write process stops writing to the named pipe but does not close it. If the FTP server cannot read any data from the named pipe for the number of seconds specified by the FIFOIOTIME value, it fails the file transfer.