note

				    Part II
getlogin() cannot be used to determine the current user name becuase
it would always fail if the current process does not have a controlling
terminal;
use getpwuid(getuid()) instead.

SUSv3 requires that PIPE_BUF be at least _POSIX_PIPE_BUF (512). An
implementation should define PIPE_BUF (in <limits.h>) and/or allow the call
fpathconf(fd, _PC_PIPE_BUF) to return the actual upper limit for atomic writes.

				    Part III
SUSv3 allows an implementation to place an upper limit on the value that can be
specified for backlog, and permits an implementation to silently round backlog
values down to this limit. SUSv3 specifies that the implementation should
advertise this limit by defining the constant SOMAXCONN in <sys/socket.h>. On
Linux, this constant is defined with the value 128. However, since kernel
2.4.25, Linux allows this limit to be adjusted at run time via the
Linux-specific /proc/sys/net/core/somaxconn file. (In earlier kernel versions,
the SOMAXCONN limit is immutable.)

If connect() fails and we wish to reattempt the connection, then SUSv3 specifies
that the portable method of doing so is to close the socket, create a new
socket, and reattempt the connection with the new socket.

The BSD-derived function bzero() is an alternative to memset() for zeroing the
contents of a structure. SUSv3 specifies bzero() and the related bcopy() (which
is similar to memmove()), but marks both functions LEGACY, noting that memset()
and memmove() are preferred. SUSv4 removes the specifications of bzero() and
bcopy().

The inet_aton() and inet_ntoa() functions convert an IPv4 address in
dotted-decimal notation to binary and vice versa. We describe these functions
primarily because they appear in historical code. Nowadays, they are obsolete.
Modern programs that need to do such conversions should use the functions that
we describe next.

The gethostbyname() function returns the binary IP address(es) corresponding to
a hostname and the getservbyname() function returns the port number
corresponding to a service name. The reverse conversions are performed by
gethostbyaddr() and getservbyport(). We describe these functions because they
are widely used in existing code. However, they are now obsolete. (SUSv3 marks
these functions obsolete, and SUSv4 removes their specifications.) New code
should use the getaddrinfo() and getnameinfo() functions (described next) for
such conversions.

On Linux, if select() returns because one or more file descriptors became
ready, and if timeout was non-NULL, then select() updates the structure to
which timeout points to indicate how much time remained until the call would
have timed out. However, this behavior is implementation-specific. SUSv3 also
allows the possibility that an implementation leaves the structure pointed to
by timeout unchanged, and most other UNIX implementations don’t modify this
structure. Portable applications that employ select() within a loop should
always ensure that the structure pointed to by timeout is initialized before
each select() call, and should ignore the information returned in the structure
after the call.