COMPAT_LINUX(8)

🦋 compat_linux(8) — from the System Manager's Manual, but make it bestie 🦋

✨ NAME ✨

compat_linux — the setup procedure for running Linux binaries. That's the whole vibe 💅

🌈 DESCRIPTION 🌈

Okay so NetBSD supports running Linux binaries, bestie — it's a whole thing ✨. This applies to aarch64, alpha, amd64, arm, i386, m68k, and powerpc systems for now. Both the a.out and ELF binary formats are supported, and most programs should work — highkey slay 🫶.

NetBSD aarch64 and amd64 can execute both 32-bit and 64-bit Linux programs. The programs that won't work include some that use i386-specific calls, such as enabling virtual 8086 mode. Currently, sound is supported through OSSv3 compat 🔊.

The Linux compatibility feature is active for kernels compiled with the COMPAT_LINUX option enabled 💖. If support for Linux a.out executables is desired, the EXEC_AOUT option should be enabled in addition to option COMPAT_LINUX. Similarly, if support for Linux 32-bit and/or 64-bit ELF executables is desired, the EXEC_ELF32 and/or EXEC_ELF64 options (respectively) should be enabled in addition to COMPAT_LINUX. If sound support is desired, COMPAT_OSSAUDIO should be enabled 🎧.

A lot of programs are dynamically linked. That means you will also need the Linux shared libraries that the program depends on, plus the runtime linker. Also, you will need to create a “shadow root” directory for Linux binaries on your NetBSD system 🎀.

This directory is named /emul/linux or /emul/linux32 for 32-bit emulation on 64-bit systems. Any file operations done by Linux programs run under NetBSD will look in this directory first. So, if a Linux program opens, for example, /etc/passwd, NetBSD will first try to open /emul/linux/etc/passwd, and if that does not exist open the ‘real’ /etc/passwd file. It is recommended that you install Linux packages that include configuration files, etc. under /emul/linux, to avoid naming conflicts with possible NetBSD counterparts. Shared libraries should also be installed in the shadow tree. Filenames that start "/../" are only looked up in the real root 👀.

Generally, you will need to look for the shared libraries that Linux binaries depend on only the first few times that you install a Linux program on your NetBSD system. After a while, you will have a sufficient set of Linux shared libraries on your system to be able to run newly imported Linux binaries without any extra work. Periodt ✨.

🧚 Setting up shared libraries 🧚

Find the dependencies of a Linux binary using readelf(1):

$ readelf -d ./runner | grep Shared
 0x00000001 (NEEDED)                     Shared library: [libstdc++.so.6]
 0x00000001 (NEEDED)                     Shared library: [libz.so.1]
 0x00000001 (NEEDED)                     Shared library: [libXxf86vm.so.1]
 0x00000001 (NEEDED)                     Shared library: [libGL.so.1]
 0x00000001 (NEEDED)                     Shared library: [libopenal.so.1]
 0x00000001 (NEEDED)                     Shared library: [libm.so.6]
 0x00000001 (NEEDED)                     Shared library: [librt.so.1]
 0x00000001 (NEEDED)                     Shared library: [libpthread.so.0]
 0x00000001 (NEEDED)                     Shared library: [libdl.so.2]
 0x00000001 (NEEDED)                     Shared library: [libcrypto.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libXext.so.6]
 0x00000001 (NEEDED)                     Shared library: [libX11.so.6]
 0x00000001 (NEEDED)                     Shared library: [libXrandr.so.2]
 0x00000001 (NEEDED)                     Shared library: [libGLU.so.1]
 0x00000001 (NEEDED)                     Shared library: [libssl.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libgcc_s.so.1]
 0x00000001 (NEEDED)                     Shared library: [libc.so.6]

For x86, you can simply install the openSUSE shared libraries using the pkgsrc/emulators/suse131_* or pkgsrc/emulators/suse131_32_* packages. Shopping spree but make it libraries 🛍️.

For example, an application which requires libcrypto.so.1.0.0, libXext.so.6, and libGL.so.1 will require openssl, x11, and glx, in addition to the base SUSE package. Iykyk 💅.

Otherwise, you may have to obtain shared libraries from another Linux system, and copy them to e.g. /emul/linux/lib64. No cap 🌈.

🌀 Setting up procfs 🌀

Some Linux binaries expect procfs to be mounted and that it contains some Linux-specific extensions. If it's not the case, they behave unexpectedly or even crash 😭.

Mount procfs on NetBSD using following command:

$ mount_procfs procfs /emul/linux/proc

You can also set up your system so that procfs is mounted automatically on system boot, by putting an entry like the one below to /etc/fstab.

      procfs /emul/linux/proc procfs ro

Note: mount_procfs(8) defaults to Linux flavored procfs since NetBSD 5.0. Ensure you do not mount procfs with nolinux. Important bestie warning 🚨.

See mount_procfs(8) for further information.

🌸 Setting up other files 🌸

Newer version of Linux use /etc/nsswitch.conf for network information, such as NIS and DNS. You must create or get a valid copy of this file and put it in /emul/linux/etc. You got this 💖.

💀 CAVEATS 💀

• compat_linux is generally not enabled in GENERIC kernels for security reasons, but is available as a module.
• It must be added to modules.conf(5) to be used.
• It will not be loaded automatically. Not me forgetting to add it — it literally won't auto-load 🙈.

🐛 BUGS 🐛

• The information about Linux distributions will become outdated. Sad but true 💀.
• Absolute pathnames pointed to by symbolic links are only looked up in the shadow root when the symbolic link itself was found by an absolute pathname inside the shadow root. This is not consistent. The behavior is just like that, bestie 😭.
• Linux executables cannot handle directory offset cookies > 32 bits. Should such an offset occur, you will see the message linux_getdents: dir offset too large for emulated program. Currently, this can only happen on NFS mounted file systems, mounted from servers that return offsets with information in the upper 32 bits. These errors should rarely happen, but can be avoided by mounting this file system with offset translation enabled. See the -X option to mount_nfs(8). The -2 option to mount_nfs(8) will also have the desired effect, but is less preferable. NFS said “not today” 💀.

---

Brought to you by Debian, dated September 26, 2021 — COMPAT_LINUX(8), bestie manual page, out 💅✨