USELIB(2) Linux Programmer's Manual USELIB(2)
uselib - load shared library
int uselib(const char *library);
Note: No declaration of this system call is provided in glibc headers;
The system call uselib() serves to load a shared library to be used by
the calling process. It is given a pathname. The address where to
load is found in the library itself. The library can have any recog-
nized binary format.
On success, zero is returned. On error, -1 is returned, and errno is
In addition to all of the error codes returned by open(2) and mmap(2),
the following may also be returned:
EACCES The library specified by library does not have read or execute
permission, or the caller does not have search permission for
one of the directories in the path prefix. (See also path_reso-
ENFILE The system-wide limit on the total number of open files has been
The file specified by library is not an executable of a known
type; for example, it does not have the correct magic numbers.
uselib() is Linux-specific, and should not be used in programs intended
to be portable.
This obsolete system call is not supported by glibc. No declaration is
provided in glibc headers, but, through a quirk of history, glibc ver-
sions before 2.23 did export an ABI for this system call. Therefore,
in order to employ this system call, it was sufficient to manually
declare the interface in your code; alternatively, you could invoke the
system call using syscall(2).
In ancient libc versions, uselib() was used to load the shared
libraries with names found in an array of names in the binary.
Since libc 4.3.2, startup code tries to prefix these names with
"/usr/lib", "/lib" and "" before giving up. In libc 4.3.4 and later
these names are looked for in the directories found in LD_LIBRARY_PATH,
and if not found there, prefixes "/usr/lib", "/lib" and "/" are tried.
From libc 4.4.4 on only the library "/lib/ld.so" is loaded, so that
this dynamic library can load the remaining libraries needed (again
using this call). This is also the state of affairs in libc5.
glibc2 does not use this call.
Since Linux 3.15, this system call is available only when the kernel is
configured with the CONFIG_USELIB option.
ar(1), gcc(1), ld(1), ldd(1), mmap(2), open(2), dlopen(3), capabili-
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Linux 2016-03-15 USELIB(2)