FS_IOC_SETFSLABEL(2const)

✨ FS_IOC_SETFSLABEL 💅

okay bestie, so this is a page from the Linux man-pages, and the manual it lives in is FS_IOC_SETFSLABEL(2const) — yes the 2const is a whole vibe, we love a section suffix. sit down, hydrate, and let's talk about naming your filesystem like it's your notes app 🌸

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🌈 NAME

FS_IOC_GETFSLABEL, FS_IOC_SETFSLABEL — get or set a filesystem label 🏷️

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🎀 LIBRARY

Standard C library (libc, -lc) 🫶

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⭐ SYNOPSIS

#include <linux/fs.h>  /* Definition of *FSLABEL* constants */
#include <sys/ioctl.h>

int ioctl(int fd, FS_IOC_GETFSLABEL, char label[FSLABEL_MAX]);
int ioctl(int fd, FS_IOC_SETFSLABEL, char label[FSLABEL_MAX]);

not me including sys/ioctl.h and linux/fs.h — yeah girl you need both, the *FSLABEL* constants live in the second one 💖

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🦋 DESCRIPTION

so if a filesystem supports online label manipulation (key words: online, meaning you don't gotta unmount anything, we love low-effort slay), you can use these ioctl(2) operations to get or set the filesystem label for the filesystem that fd lives on.

FS_IOC_SETFSLABEL is not for the girlies without clearance tho — it requires privilege, specifically CAP_SYS_ADMIN 👑

basically: reading your label is free, changing it needs the keys to the kingdom. periodt.

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💜 RETURN VALUE

• On success, zero is returned ✨
• On error, -1 is returned, and errno gets set to tell you what went wrong 😭

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🙈 ERRORS

possible errors include (but are not limited to) the following — so like, don't come for me if you get a weird one:

• EFAULT — label references an inaccessible memory area 😵 (your pointer said "trust me" and lied)
• EINVAL — the specified label exceeds the maximum label length for the filesystem 📏 too long, bestie, it won't fit
• ENOTTY — this can appear if the filesystem does not support online label manipulation 🚫 tier: this filesystem said "no 💅"
• EPERM — the calling process does not have sufficient permissions to set the label 🔒 (see: CAP_SYS_ADMIN, or rather, your lack thereof)

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🌸 STANDARDS

Linux. that's it. that's the standard. iykyk 🐧

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💀 HISTORY

Linux 4.18. ✨

they were previously known as BTRFS_IOC_GET_FSLABEL and BTRFS_IOC_SET_FSLABEL and were private to Btrfs — so yeah, they got a glow-up, went public, changed their names. main character arc fr fr 👑

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🔥 NOTES

okay this part matters, listen up:

• the maximum string length for this interface is FSLABEL_MAX, and that count includes the terminating null byte ('\0') 🫶
• filesystems have differing maximum label lengths, and those may or may not include the terminating null — so like, it's giving inconsistent, no cap
• the string you hand to FS_IOC_SETFSLABEL must always be null-terminated ⚠️
• the string returned by FS_IOC_GETFSLABEL will always be null-terminated ✅

bestie if you forget the '\0' on the set side you're gonna have a bad time. that's not me being dramatic, that's just the interface.

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💖 SEE ALSO

• ioctl(2)
• blkid(8)

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that's the whole page, you ate it 🍓 go label something responsibly, and remember: CAP_SYS_ADMIN or it's a no from the kernel 👑

this has been Linux man-pages 6.20, dated 2026-02-08, page FS_IOC_SETFSLABEL(2const) — mwah, ily, bye 💅✨