ioperm(2)

💖 ioperm(2) — set I/O port permissions 💖

okay bestie, welcome to the ioperm page from the System Calls Manual 🎀 this one's short and sweet, let's get into it 💅

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📚 LIBRARY

Standard C library (libc, -lc) 🫶

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✨ SYNOPSIS

#include <sys/io.h>

int ioperm(unsigned long from, unsigned long num, int turn_on);

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🌸 DESCRIPTION

so basically, ioperm() sets the calling thread's access permission for num ports, starting from port address from 🦋

if turn_on is nonzero, permission for those ports gets turned on; otherwise it gets turned off. and here's the tea: if turn_on is nonzero, the calling thread must be privileged — like, it needs CAP_SYS_RAWIO 👑

okay now the lore: before Linux 2.6.8, only the first 0x3ff I/O ports could be specified this way. wanted more? you had to use the iopl(2) system call instead, with a level argument of 3 😭 since Linux 2.6.8, 65,536 I/O ports can be specified. we love growth 💖

permissions are inherited by the child created by fork(2) — but peek at HISTORY for the plot twist 🙈 permissions are preserved across execve(2), which is lowkey the whole point: it's useful for giving port access permissions to unprivileged programs ✨

this call is mostly for the i386 architecture. on many other architectures it does not exist, or it will always return an error 💀

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🔥 RETURN VALUE

win? you get zero 🎉 lose? you get -1 back, and errno is set to tell you what went wrong 💅

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💀 ERRORS

• EINVAL — invalid values for from or num 🙈
• EIO — (on PowerPC) this call is not supported, sorry bestie 😭
• ENOMEM — out of memory 😵
• EPERM — the calling thread has insufficient privilege 👑🚫

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⭐ VERSIONS

glibc has an ioperm() prototype in both <sys/io.h> and <sys/perm.h>. avoid the latter — it is available on i386 only 🚩

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🌈 STANDARDS

Linux ✨

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🕰️ HISTORY

before Linux 2.4, permissions were not inherited by a child created by fork(2). wild, right? 😳

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🧚 NOTES

the /proc/ioports file shows the I/O ports that are currently allocated on the system 👀 handy!!

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👀 SEE ALSO

iopl(2), outb(2), capabilities(7)

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and that's the whole page, no cap 💖 go forth and permission responsibly bestie 🫶

okay love u bye — this was pulled from Linux man-pages 6.20, dated 2026-10-11 🎀💜✨