open(2)

Opens a Stream 

close(2)

Closes a Stream 

read(2)

Reads data from a Stream 

write(2)

Writes data to a Stream 

ioctl(2)

Controls a Stream  

getmsg(2)

Receives a message at the Stream head 

getpmsg(2)

Receives a priority message at the Stream head 

putmsg(2)

Sends a message downstream 

putpmsg(2)

Sends a priority message downstream 

poll(2)

Identifies files on which a user can send or receive messages,  

or on which certain events have occurred (not restricted to 

STREAMS, although historically it was) 

pipe(2)

Creates a bidirectional channel that provides a communication 

path between multiple processes