F_GETPIPE_SZ(2const)                                      F_GETPIPE_SZ(2const)

NAME
       F_GETPIPE_SZ, F_SETPIPE_SZ - get/set the capacity of a pipe

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #define _GNU_SOURCE
       #include <fcntl.h>

       int fcntl(int fd, F_SETPIPE_SZ, int arg);
       int fcntl(int fd, F_GETPIPE_SZ);

DESCRIPTION
       F_SETPIPE_SZ
              Change the capacity of the pipe referred to by fd to be at least
              arg bytes.  An unprivileged process can adjust the pipe capacity
              to any value between the system page size and the limit defined
              in /proc/sys/fs/pipe-max-size (see proc_sys_fs(5)).  Attempts to
              set the pipe capacity below the page size are silently rounded
              up to the page size.  Attempts by an unprivileged process to set
              the pipe capacity above the limit in /proc/sys/fs/pipe-max-size
              yield the error EPERM; a privileged process (CAP_SYS_RESOURCE)
              can override the limit.

              When allocating the buffer for the pipe, the kernel may use a
              capacity larger than arg, if that is convenient for the
              implementation.  (In the current implementation, the allocation
              is the next higher power-of-two page-size multiple of the
              requested size.)  The actual capacity (in bytes) that is set is
              returned as the function result.

              Attempting to set the pipe capacity smaller than the amount of
              buffer space currently used to store data produces the error
              EBUSY.

              Note that because of the way the pages of the pipe buffer are
              employed when data is written to the pipe, the number of bytes
              that can be written may be less than the nominal size, depending
              on the size of the writes.

       F_GETPIPE_SZ
              Return (as the function result) the capacity of the pipe
              referred to by fd.

RETURN VALUE
       The pipe capacity.

       On error, -1 is returned, and errno is set to indicate the error.

ERRORS
       See fcntl(2).

       EBUSY  op is F_SETPIPE_SZ and the new pipe capacity specified in arg is
              smaller than the amount of buffer space currently used to store
              data in the pipe.

       EPERM  op is F_SETPIPE_SZ and the soft or hard user pipe limit has been
              reached; see pipe(7).

STANDARDS
       Linux.

HISTORY
       Linux 2.6.35.

SEE ALSO
       fcntl(2)

Linux man-pages 6.15              2025-07-20              F_GETPIPE_SZ(2const)