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IOPERM(2)		   Linux Programmer's Manual		     IOPERM(2)


ioperm - set port input/output permissions


#include <unistd.h> /* for libc5 */ #include <sys/io.h> /* for glibc */ int ioperm(unsigned long from, unsigned long num, int turn_on);


Ioperm sets the port access permission bits for the process for num bytes starting from port address from to the value turn_on. The use of ioperm() requires root privileges. Only the first 0x3ff I/O ports can be specified in this manner. For more ports, the iopl() function must be used. Permissions are not inherited on fork(), but on exec() they are. This is useful for giving port access permissions to non-privileged tasks. This call is mostly for the i386 architecture. On many other architec- tures it does not exist or will always return an error.


On success, zero is returned. On error, -1 is returned, and errno is set appropriately.


EINVAL Invalid values for from or num. EIO (on ppc) This call is not supported. EPERM The calling process has insufficient privilege to call ioperm(); the CAP_SYS_RAWIO capability is required.


ioperm() is Linux specific and should not be used in programs intended to be portable.


Libc5 treats it as a system call and has a prototype in <unistd.h>. Glibc1 does not have a prototype. Glibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on i386 only.


iopl(2), capabilities(7) Linux 2.6.6 2004-05-27 IOPERM(2)

1994 Man-cgi 1.15, Panagiotis Christias <>