personality(2)

💖 personality(2) 💖

okay bestie, sit DOWN, we're talking about personality(2) — yes it's really called that, yes it's a system call, and yes it's in the System Calls Manual, and it's about to be your new obsession 🫶

🌸 NAME 🌸

personality — set the process execution domain ✨

🎀 LIBRARY 🎀

Standard C library (libc, -lc) — the moment you've all been waiting for 💅

👑 SYNOPSIS 👑

#include <sys/personality.h>

int personality(unsigned long persona);

✨ DESCRIPTION ✨

so. Linux supports different execution domains (aka personalities) for every single process, no cap. Among other things, execution domains tell Linux how to map signal numbers into signal actions. The whole execution domain system is literally how Linux gives you limited support for binaries that were compiled under other UNIX-like operating systems. it's giving "we can speak your ex's language, but only a little" 😭

If persona is not 0xffffffff, then personality() sets the caller's execution domain to the value you specified in persona. And if you pass persona as 0xffffffff? That's the ✨look-but-don't-touch✨ move — it's how you retrieve the current persona without changing it. iconic behavior honestly.

A list of the available execution domains can be found in <sys/personality.h>. The execution domain is a 32-bit value, and the way it's sliced up is so important bestie:

• the top three bytes are set aside for flags that make the kernel modify the behavior of certain system calls, so as to emulate historical or architectural quirks
• the least significant byte is the value defining the personality the kernel should assume 👑

The flag values are as follows:

• ADDR_COMPAT_LAYOUT (since Linux 2.6.9) — with this flag set, provide legacy virtual address space layout.
• ADDR_NO_RANDOMIZE (since Linux 2.6.12) — with this flag set, disable address-space-layout randomization.
• ADDR_LIMIT_32BIT (since Linux 2.2) — limit the address space to 32 bits.
• ADDR_LIMIT_3GB (since Linux 2.4.0) — with this flag set, use 0xc0000000 as the offset at which to search a virtual memory chunk on mmap(2); otherwise use 0xffffe000. Applies to 32-bit x86 processes only.
• FDPIC_FUNCPTRS (since Linux 2.6.11) — user-space function pointers to signal handlers point to descriptors. Applies only to ARM if BINFMT_ELF_FDPIC and SuperH.
• MMAP_PAGE_ZERO (since Linux 2.4.0) — map page 0 as read-only (to support binaries that depend on this SVr4 behavior).
• READ_IMPLIES_EXEC (since Linux 2.6.8) — with this flag set, PROT_READ implies PROT_EXEC for mmap(2).
• SHORT_INODE (since Linux 2.4.0) — No effect. 💀 yeah. nothing. it does nothing.
• STICKY_TIMEOUTS (since Linux 1.2.0) — with this flag set, select(2), pselect(2), and ppoll(2) do not modify the returned timeout argument when interrupted by a signal handler.
• UNAME26 (since Linux 3.1) — have uname(2) report a 2.6.(40+x) version number rather than a MAJOR.x version number. Added as a stopgap measure to support broken applications that could not handle the kernel version-numbering switch from Linux 2.6.x to Linux 3.x. poor little meow meows 🐈
• WHOLE_SECONDS (since Linux 1.2.0) — No effect. also nothing. we love a flag that simply exists 🧚

And now, the available execution domains ✨:

• PER_BSD (since Linux 1.2.0) — BSD. (No effects.)
• PER_HPUX (since Linux 2.4) — Support for 32-bit HP/UX. This support was never complete, and was dropped so that since Linux 4.0, this value has no effect.
• PER_IRIX32 (since Linux 2.2) — IRIX 5 32-bit. Never fully functional; support dropped in Linux 2.6.27. Implies STICKY_TIMEOUTS.
• PER_IRIX64 (since Linux 2.2) — IRIX 6 64-bit. Implies STICKY_TIMEOUTS; otherwise no effect.
• PER_IRIXN32 (since Linux 2.2) — IRIX 6 new 32-bit. Implies STICKY_TIMEOUTS; otherwise no effect.
• PER_ISCR4 (since Linux 1.2.0) — Implies STICKY_TIMEOUTS; otherwise no effect.
• PER_LINUX (since Linux 1.2.0) — Linux. (the main character, obviously 👑)
• PER_LINUX32 (since Linux 2.2) — uname(2) returns the name of the 32-bit architecture in the machine field ("i686" instead of "x86_64", &c.).
  • Under ia64 (Itanium), processes with this personality don't have the O_LARGEFILE open(2) flag forced.
  • Under 64-bit ARM, setting this personality is forbidden if execve(2)ing a 32-bit process would also be forbidden (cf. the allow_mismatched_32bit_el0 kernel parameter and Documentation/arm64/asymmetric-32bit.rst).
• PER_LINUX32_3GB (since Linux 2.4) — Same as PER_LINUX32, but implies ADDR_LIMIT_3GB.
• PER_LINUX_32BIT (since Linux 2.0) — Same as PER_LINUX, but implies ADDR_LIMIT_32BIT.
• PER_LINUX_FDPIC (since Linux 2.6.11) — Same as PER_LINUX, but implies FDPIC_FUNCPTRS.
• PER_OSF4 (since Linux 2.4) — OSF/1 v4. No effect since Linux 6.1, which removed a.out binary support. Before, on alpha, would clear top 32 bits of iov_len in the user's buffer for compatibility with old versions of OSF/1 where iov_len was defined as. int.
• PER_OSR5 (since Linux 2.4) — SCO OpenServer 5. Implies STICKY_TIMEOUTS and WHOLE_SECONDS; otherwise no effect.
• PER_RISCOS (since Linux 2.3.7; macro since Linux 2.3.13) — Acorn RISC OS/Arthur (MIPS). No effect. Up to Linux 4.0, would set the emulation altroot to /usr/gnemul/riscos (cf. PER_SUNOS, below). Before then, up to Linux 2.6.3, just Arthur emulation.
• PER_SCOSVR3 (since Linux 1.2.0) — SCO UNIX System V Release 3. Same as PER_OSR5, but also implies SHORT_INODE.
• PER_SOLARIS (since Linux 2.4) — Solaris. Implies STICKY_TIMEOUTS; otherwise no effect.
• PER_SUNOS (since Linux 2.4.0) — Sun OS. Same as PER_BSD, but implies STICKY_TIMEOUTS. Prior to Linux 2.6.26, diverted library and dynamic linker searches to /usr/gnemul. Buggy, largely unmaintained, and almost entirely unused. 🚩 bestie this one is a red flag, not a green one.
• PER_SVR3 (since Linux 1.2.0) — AT&T UNIX System V Release 3. Implies STICKY_TIMEOUTS and SHORT_INODE; otherwise no effect.
• PER_SVR4 (since Linux 1.2.0) — AT&T UNIX System V Release 4. Implies STICKY_TIMEOUTS and MMAP_PAGE_ZERO; otherwise no effect.
• PER_UW7 (since Linux 2.4) — UnixWare 7. Implies STICKY_TIMEOUTS and MMAP_PAGE_ZERO; otherwise no effect.
• PER_WYSEV386 (since Linux 1.2.0) — WYSE UNIX System V/386. Implies STICKY_TIMEOUTS and SHORT_INODE; otherwise no effect.
• PER_XENIX (since Linux 1.2.0) — XENIX. Implies STICKY_TIMEOUTS and SHORT_INODE; otherwise no effect.

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🦋 RETURN VALUE 🦋

On success, the previous persona is returned. ✨

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

💜 ERRORS 💜

• EINVAL — The kernel was unable to change the personality.

🌈 STANDARDS 🌈

Linux. 🐧 (that's it. that's the standard.)

🍓 HISTORY 🍓

Linux 1.1.20, glibc 2.3.

⭐ SEE ALSO ⭐

setarch(8) — go read it bestie, iykyk 💅

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and that's the whole page, periodt. 🎀 this little slice of lore came to you from Linux man-pages 6.20, dated 2026-02-08, so if you're citing it in the group chat, that's the version. stay slaying, stay sticky-timeout-ing 🫶✨💖