Rust compilation by codex results in hard-linking files across file systems #8636
Description
What version of Codex is running?
codex-cli 0.77.0
What subscription do you have?
Pro
Which model were you using?
gpt-5.2-codex
What platform is your computer?
Linux 5.15.197-1-MANJARO x86_64 unknown
What issue are you seeing?
When codex attempts to build even a simple Rust program, compiler complains about hard linking failures. In this example this is just a warning:
› Make this print "Hello all" instead of "Hello world". Then build and invoke it.
• Explored
└ List ls
Search Hello in src
Read main.rs
• Edited src/main.rs (+1 -1)
1 fn main() {
2 - println!("Hello, world!");
2 + println!("Hello all");
3 }
• Ran cargo build
└ Compiling link_test v0.1.0 (/home/mikhail/code/link_test)
warning: hard linking files in the incremental compilation cache failed. copying files instead. consider moving the cache directory to a file system which supports hard linking in session dir `/home/mikhail/code/link_test/target/debug/incremental/
… +2 lines
warning: `link_test` (bin "link_test") generated 1 warning
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s
• Ran cargo run
└ warning: hard linking files in the incremental compilation cache failed. copying files instead. consider moving the cache directory to a file system which supports hard linking in session dir `/home/mikhail/code/link_test/target/debug/incremental/
link_test-14ijk4ciabvy6/s-heeghrr4y3-08ahhzm-working`
… +3 lines
Running `target/debug/link_test`
Hello all
─ Worked for 26s ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
• Updated the greeting in src/main.rs to print Hello all, then built and ran the binary.
Command output (invocation):
Hello all
Note: cargo emitted a warning about hard linking in the incremental cache; it still built and ran successfully.
If I run this myself in a shell (or even in codex prompt with !) then it doesn't exhibit this behavior.
What steps can reproduce the bug?
Create a small Rust binary then run codex on it:
cargo new --bin link_test
cd link_test
codex
And then give it the instructions above.
What is the expected behavior?
It can build without warnings.
Additional information
Mount points:
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
sys on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
dev on /dev type devtmpfs (rw,nosuid,relatime,size=8027244k,nr_inodes=2006811,mode=755,inode64)
run on /run type tmpfs (rw,nosuid,nodev,relatime,mode=755,inode64)
efivarfs on /sys/firmware/efi/efivars type efivarfs (rw,nosuid,nodev,noexec,relatime)
/dev/nvme0n1p2 on / type ext4 (rw,noatime)
securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,inode64)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=600,ptmxmode=000)
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate,memory_recursiveprot)
pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)
bpf on /sys/fs/bpf type bpf (rw,nosuid,nodev,noexec,relatime,mode=700)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=38,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=23587)
debugfs on /sys/kernel/debug type debugfs (rw,nosuid,nodev,noexec,relatime)
mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime)
hugetlbfs on /dev/hugepages type hugetlbfs (rw,nosuid,nodev,relatime,pagesize=2M)
tracefs on /sys/kernel/tracing type tracefs (rw,nosuid,nodev,noexec,relatime)
configfs on /sys/kernel/config type configfs (rw,nosuid,nodev,noexec,relatime)
fusectl on /sys/fs/fuse/connections type fusectl (rw,nosuid,nodev,noexec,relatime)
none on /run/credentials/systemd-journald.service type ramfs (ro,nosuid,nodev,noexec,relatime,nosymfollow,mode=700)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,size=8044920k,nr_inodes=1048576,inode64)
/dev/nvme0n1p4 on /boot/efi type vfat (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,nosuid,nodev,noexec,relatime)
tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=1608980k,nr_inodes=402245,mode=700,uid=1000,gid=1000,inode64)
/dev/mapper/home-mikhail on /home/mikhail type ext4 (rw,relatime)
gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000)
gdrive: on /home/mikhail/mnt/gdrive type fuse.rclone (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000,allow_other)
portal on /run/user/1000/doc type fuse.portal (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000)
$ rustup --version
rustup 1.28.2 (e4f3ad6f8 2025-04-28)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.90.0 (1159e78c4 2025-09-14)`
$ rustc --version
rustc 1.90.0 (1159e78c4 2025-09-14)