Page MenuHomeFreeBSD
Files F153072180

D33738.id101164.diff
No OneTemporary
Actions

D33738.id101164.diff
View Options

diff --git a/documentation/content/en/books/handbook/linuxemu/_index.adoc b/documentation/content/en/books/handbook/linuxemu/_index.adoc
--- a/documentation/content/en/books/handbook/linuxemu/_index.adoc
+++ b/documentation/content/en/books/handbook/linuxemu/_index.adoc
@@ -1,9 +1,9 @@
---
-title: Chapter 10. Linux® Binary Compatibility
+title: Chapter 10. Linux Binary Compatibility
part: Part II. Common Tasks
prev: books/handbook/printing
next: books/handbook/wine
-description: FreeBSD provides binary compatibility with Linux®, allowing users to install and run most Linux® binaries on a FreeBSD system without having to first modify the binary
+description: FreeBSD provides binary compatibility with Linux, allowing users to install and run most Linux binaries on a FreeBSD system without having to first modify the binary
tags: ["linux", "linuxulator", "emulation", "binary", "compatibility"]
showBookMenu: true
weight: 13
@@ -51,16 +51,13 @@
[[linuxemu-synopsis]]
== Synopsis
-FreeBSD provides binary compatibility with Linux(R), allowing users to install and run most Linux binaries on a FreeBSD system without having to first modify the binary.
-It has even been reported that, in some situations, Linux binaries perform better on FreeBSD than they do on Linux.
+FreeBSD provides optional binary compatibility with Linux(R), allowing users to install
+and run unmodified Linux binaries.
+It is available for i386, amd64, and arm64 architectures.
-However, some Linux-specific operating system features are not supported under FreeBSD.
-For example, Linux binaries will not work on FreeBSD if they overly use i386(TM) specific calls, such as enabling virtual 8086 mode.
-
-[NOTE]
-====
-Support for 64-bit binary compatibility with Linux was added in FreeBSD 10.3.
-====
+Some Linux-specific operating system features are not yet supported;
+this mostly happens with functionality specific to hardware or related
+to system management, such as cgroups or namespaces.
After reading this chapter, you will know:
@@ -76,76 +73,117 @@
[[linuxemu-lbc-install]]
== Configuring Linux Binary Compatibility
-By default, Linux libraries are not installed and Linux binary compatibility is not enabled.
-Linux libraries can either be installed manually or from the FreeBSD Ports Collection.
+By default, Linux binary compatibility is not enabled. To enable it at boot time,
+add this line to [.filename]#/etc/rc.conf#:
-Before attempting to build the port, load the Linux kernel module, otherwise the build will fail:
+[.programlisting]
+....
+linux_enable="YES"
+....
+To enable it without rebooting, run this command:
[source,shell]
....
-# kldload linux
+# service linux start
....
-For 64-bit compatibility:
+The [.filename]#/etc/rc.d/linux# script will load neccessary kernel modules and mount filesystems
+expected by Linux applications under [.filename]#/compat/linux#. This is enough for statically
+linked Linux binaries to work. They can be started in the same way native FreeBSD binaries can;
+they behave almost exactly like native processes and can be traced and debugged the usual way.
+
+Linux binaries linked dynamically (which is the vast majority) also require Linux shared libraries
+to be installed - they can run on top of FreeBSD kernel, but they cannot use FreeBSD libraries;
+this is similar to how 32-bit binaries cannot use native 64-bit libraries.
+There are several ways of providing those libraries: one can copy them over from existing
+Linux installation, install from FreeBSD packages, or install using deboostrap(8), and others.
+
+[[linuxemu-packages]]
+== CentOS Userspace from FreeBSD Packages
+
+The easiest way to install Linux libraries is to install package:emulators/linux_base-c7[]
+package or port:
[source,shell]
....
-# kldload linux64
+# pkg install linux_base-c7
....
-To verify that the module is loaded:
-
+FreeBSD provides packages for some Linux binary applications. For example, to install
+Sublime Text, run this command:
[source,shell]
....
-% kldstat
- Id Refs Address Size Name
- 1 2 0xc0100000 16bdb8 kernel
- 7 1 0xc24db000 d000 linux.ko
+# pkg install linux-sublime
....
-The package:emulators/linux_base-c7[] package or port is the easiest way to install a base set of Linux libraries and binaries on a FreeBSD system.
-To install the port:
+[[linuxemu-debootstrap]]
+== Debian / Ubuntu Userspace with deboostrap(8)
-[source,shell]
+An alternative way of providing Linux shared libraries is by using package:sysutils/debootstrap[].
+This has the advantage of providing a full Debian or Ubuntu distribution. To use it, follow the
+instructions at FreeBSD Wiki: https://wiki.freebsd.org/LinuxJails[FreeBSD Wiki - Linux Jails].
+
+It is possible to debootstrap into [.filename]#/compat/linux#, but it is discouraged to avoid
+collisions with files installed from FreeBSD ports and packages. Instead, derive the directory
+name from distribution or version name, e.g. [.filename]#/compat/ubuntu#. If you want to use
+it to provide Linux shared libraries without having to explicitly use chroot or jails,
+point the kernel at it by updating the `compat.linux.emul_path` sysctl and adding a line like
+this to [.filename]#/etc/sysctl.conf#:
+
+[.programlisting]
....
-# pkg install emulators/linux_base-c7
+compat.linux.emul_path="/compat/ubuntu"
....
-For Linux compatibility to be enabled at boot time, add this line to [.filename]#/etc/rc.conf#:
+Afterwards chroot(8) into the newly created directory and install software in a way typical
+for the Linux distribution you have debootstrapped, for example:
-[.programlisting]
+[source,shell]
....
-linux_enable="YES"
+# chroot /compat/ubuntu /bin/bash
+root@hostname:/# apt update
....
-On 64-bit machines, [.filename]#/etc/rc.d/abi# will automatically load the module for 64-bit emulation.
+[[linuxemu-advanced]]
+== Advanced Topics
-Since the Linux binary compatibility layer has gained support for running both 32- and 64-bit Linux binaries (on 64-bit x86 hosts), it is no longer possible to link the emulation functionality statically into a custom kernel.
+Linux compatibility layer is a work in progress. Consult
+https://wiki.freebsd.org/Linuxulator[FreeBSD Wiki - Linuxulator] for more information.
-For some applications, [.filename]#/compat/linux/proc#, [.filename]#/compat/linux/sys#, and [.filename]#/compat/linux/dev/shm# may need to be mounted.
-Add this line to [.filename]#/etc/fstab#:
+List of all sysctl knobs can be found in man:linux[4] man page.
+Some applications require specific filesystems to be mounted.
+This is normally handled by [.filename]#/etc/rc.d/linux# script, but can be disabled
+by adding this line to [.filename]#/etc/rc.conf#:
+
+[.programlisting]
....
-linprocfs /compat/linux/proc linprocfs rw 0 0
-linsysfs /compat/linux/sys linsysfs rw 0 0
-tmpfs /compat/linux/dev/shm tmpfs rw,mode=1777 0 0
+linux_mounts_enable="NO"
....
-Then mount the filesystem accordingly:
+Filesystems mounted by the rc script will not work for Linux processes
+inside chroots or jails; one can manually configure them in [.filename]#/etc/fstab#:
+....
+devfs /compat/linux/dev devfs rw,late 0 0
+tmpfs /compat/linux/dev/shm tmpfs rw,late,size=1g,mode=1777 0 0
+fdescfs /compat/linux/dev/fd fdescfs rw,late,linrdlnk 0 0
+linprocfs /compat/linux/proc linprocfs rw,late 0 0
+linsysfs /compat/linux/sys linsysfs rw,late 0 0
+....
-[source,shell]
-----
-# mount /compat/linux/sys
-# mount /compat/linux/proc
-# mount /compat/linux/dev/shm
-----
+Since the Linux binary compatibility layer has gained support for running both 32- and 64-bit Linux binaries (on 64-bit x86 hosts), it is no longer possible to link the emulation functionality statically into a custom kernel.
[[linuxemu-libs-manually]]
=== Installing Additional Libraries Manually
+[NOTE]
+====
+For userspaces created with debootstrap(8), use the instructions above instead.
+====
+
If a Linux application complains about missing shared libraries after configuring Linux binary compatibility, determine which shared libraries the Linux binary needs and install them manually.
-From a Linux system, `ldd` can be used to determine which shared libraries the application needs.
+From a Linux system using the same CPU architecture, `ldd` can be used to determine which shared libraries the application needs.
For example, to check which shared libraries `linuxdoom` needs, run this command from a Linux system that has Doom installed:
[source,shell]
@@ -202,10 +240,13 @@
Generally, one will need to look for the shared libraries that Linux binaries depend on only the first few times that a Linux program is installed on FreeBSD.
After a while, there will be a sufficient set of Linux shared libraries on the system to be able to run newly installed Linux binaries without any extra work.
-=== Installing Linux ELF Binaries
+=== Branding Linux ELF Binaries
-ELF binaries sometimes require an extra step.
-When an unbranded ELF binary is executed, it will generate an error message:
+FreeBSD kernel uses several methods to determine if the binary to be executed is a Linux
+one: it checks the brand in the ELF file header, looks for known ELF interpreter paths
+and checks ELF notes; finally, by default, unbranded ELF executables are assumed to be Linux
+anyway. Should all those methods fail, an attempt to execute the binary might result in error
+message:
[source,shell]
....
@@ -221,8 +262,6 @@
% brandelf -t Linux my-linux-elf-binary
....
-Since the GNU toolchain places the appropriate branding information into ELF binaries automatically, this step is usually not necessary.
-
=== Installing a Linux RPM Based Application
To install a Linux RPM-based application, first install the package:archivers/rpm4[] package or port.
@@ -260,14 +299,14 @@
Remove `bind` if a name server is not configured using [.filename]#/etc/resolv.conf#.
[[linuxemu-advanced]]
-== Advanced Topics
+=== Miscellaneous
This section describes how Linux binary compatibility works and is based on an email written to {freebsd-chat} by Terry Lambert mailto:tlambert@primenet.com[tlambert@primenet.com] (Message ID: `<199906020108.SAA07001@usr09.primenet.com>`).
FreeBSD has an abstraction called an "execution class loader".
This is a wedge into the man:execve[2] system call.
-Historically, the UNIX(R) loader examined the magic number (generally the first 4 or 8 bytes of the file) to see if it was a binary known to the system, and if so, invoked the binary loader.
+Historically, the UNIX loader examined the magic number (generally the first 4 or 8 bytes of the file) to see if it was a binary known to the system, and if so, invoked the binary loader.
If it was not the binary type for the system, the man:execve[2] call returned a failure, and the shell attempted to start executing it as shell commands.
The assumption was a default of "whatever the current shell is".
@@ -296,7 +335,7 @@
Linux mode dynamically _reroots_ lookups.
This is, in effect, equivalent to `union` to file system mounts.
-First, an attempt is made to lookup the file in [.filename]#/compat/linux/original-path#.
+First, an attempt is made to look up the file in [.filename]#/compat/linux/original-path#.
If that fails, the lookup is done in [.filename]#/original-path#.
This makes sure that binaries that require other binaries can run.
For example, the Linux toolchain can all run under Linux ABI support.
@@ -308,5 +347,5 @@
The FreeBSD _glue_ functions are statically linked into the kernel, and the Linux _glue_ functions can be statically linked, or they can be accessed via a kernel module.
Technically, this is not really emulation, it is an ABI implementation.
-It is sometimes called "Linux emulation" because the implementation was done at a time when there was no other word to describe what was going on.
+It is sometimes called "Linux emulation" because the implementation was done at a time when there was no other word to describe what was going on.
Saying that FreeBSD ran Linux binaries was not true, since the code was not compiled in.

File Metadata

Mime Type
text/plain
Expires
Sun, Apr 19, 11:18 PM (12 h, 35 m)
Storage Engine
blob
Storage Format
Raw Data
Storage Handle
31806956
Default Alt Text
D33738.id101164.diff (12 KB)

Event Timeline