NS_GET_OWNER_UID(2const)

👑 NS_GET_OWNER_UID 💅

okay bestie, pull up a chair, because today we're reading the manual page for NS_GET_OWNER_UID, from the <rainbow>NS_GET_OWNER_UID(2const)</rainbow> corner of the Linux manual. it's giving detective energy, it's giving "who made this namespace", it's giving everything. 🕵️♀️✨

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✨ NAME ✨

NS_GET_OWNER_UID — the glow-up tool for discovering the owner of a user namespace 💖

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🔮 SYNOPSIS 🔮

#include <linux/nsfs.h>  /* Definition of NS_GET_OWNER_UID */
#include <sys/ioctl.h>

int ioctl(int fd, NS_GET_OWNER_UID, uid_t *uid);

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🦋 DESCRIPTION 🦋

so, the NS_GET_OWNER_UID operation is literally your backstage pass 🎟️ — you use it to discover the owner user ID of a user namespace. and what does "owner user ID" mean exactly?? it's the effective user ID of the process that created the user namespace. like, the founding mother of the whole thing. the main character who started it all. 👑

fd refers to a /proc/pid/ns/user file. that's the file you're pointing at, bestie. 🫶

the owner user ID gets returned in the uid_t pointed to by the third argument. so you hand it a pointer, it fills that pointer with the truth. no cap. 💅

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🎀 RETURN VALUE 🎀

• on success, 0 is returned. slay. ✅
• on error, -1 is returned, and errno is set to indicate the error. 😭

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💀 ERRORS 💀

• EINVAL — fd does not refer to a user namespace. like, wrong file, wrong vibe, wrong everything. this is not the namespace you're looking for. 🙈

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🌈 STANDARDS 🌈

Linux. that's it. that's the whole standard. periodt. 💅

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⭐ HISTORY ⭐

Linux 4.11. she's been iconic since 4.11, we love a legacy queen. 👑

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🌸 SEE ALSO 🌸

• ioctl(2)
• ioctl_nsfs(2)

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and that's the whole page, bestie!! this lil gem is from the Linux man-pages 6.20 era, dated 2026-02-08, and fr fr it's been a pleasure reading it with you. go forth, find out who owns your namespaces, and stay iconic. 🦋💖✨