WSL - Windows SubSytem For Linux
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In this talk, we'll dive into WSL (Windows SubSystem For Linux). We'll look at the internals, tooling, tips/tricks/gotchas & upcoming roadmap for WSL2. Author: Mithun Shanbhag
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WSL - Windows SubSytem For Linux
- 18. twitter: @MithunShanbhagblog: mithunshanbhag.github.io Image attribution: Microsoft (WSL Documentation)
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- 27. twitter: @MithunShanbhagblog: mithunshanbhag.github.io Image attribution: Microsoft (WSL Blog)
- 28. twitter: @MithunShanbhagblog: mithunshanbhag.github.io Image attribution: Microsoft (Build 2019)
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Editor's Notes
- WSL is mainly for development scenarios. NOT for production scenarios. Major adv is Windows <-> Linux interop
- 1. WSL2 requires windows insider build 18917 or higher. 2. You can install multiple linux distros (only one will be default). 2. Can be installed in one of the following ways: Download & install from Microsoft store. Download & install APPX. 2. Installation on Win Server has additional steps (unzip appx file & run installer).
- 7. Run “ls -l /usr/bin/wsl*“ to see list of wsl utilities wslsys wslfetch –splash (takes a bit of time) wslvar –getsys 8. Run “sudo /etc/init.d/docker start” to start docker Docker ps Docker images Docker run –it alpine /bin/sh
- 1. WSL2 requires windows insider build 18917 or higher. 2. You can install multiple linux distros (only one will be default). 2. Can be installed in one of the following ways: Download & install from Microsoft store. Download & install APPX. 2. Installation on Win Server has additional steps (unzip appx file & run installer).
- @todo: Show examples with “--set-version” and “--unregister”.
- 1. The \\WSL$ is facilitated by 9P server (running inside /init)
- 5.1. To clarify: - If linux command prompt is under /mnt/xyz, then the windows command gets the same as its current directory. - If linux command prompt is elsewhere, then the windows command gets %WINDIR% as its current directory.
- - /etc/fstab is processed on WSL start. /etc/fstab is a file where you can declare other filesystems, like an SMB share. Thus, you can mount these filesystems automatically in WSL on start up. - /etc/hosts file, contains hostname <-> ip mapping - /etc/resolv.conf file, contains list of DNS resolution servers
- 1.2. Not really a limitation. More like a blessing. 3.1. We’ll explore more in detail in WSL2 architecture.
- @todo: wslpath
- NTDLL, PEB, TEB etc are the standard interfaces between user-mode processes and the NT kernel. 3. Pico processes do not interact with NT Kernel directly. 3. When NT Kernel detect a process without PEB/TEB/NTDLL, it asks LXSS/LXCore to interact with it instead. 3. @todo: The pico providers (LXSS/LXCore) provide POSIX compliance for NT Kernel?
- 1. VFS abstracts all file system operations. 1. Various ile systems are mounted on different directories in the VFS namespace. 1. VFS utilizes a number of data structures - inodes - directory entries - file objects - file descriptors, - special files (device files, FIFOs, sockets, symbolic links).
- 2. The first time an NT process requests launching a Linux binary an instance is created. Once the last NT client closes, the Linux instance is terminated. Notes on /init: /init is a multi-purpose binary that was written by Microsoft and is shipped as a binary resource contained in LxssManager.dll. When /init is launched, it first checks its PID. If the PID is 1, /init will run in "daemon mode" where it essentially the Lxss Manger service’s endpoint inside a WSL instance. If the PID is not 1, /init runs as "binfmt_misc interpreter mode" which allows launching NT binaries.
- Advantages of WSL2 over WSL - Faster file access - Full kernel implementation 7. Key thing to remember is that linux is running side-by-side with windows (and not inside it).
- 4. The EXT4 VHD is mapped in. Then the /init process is run.
- Important to note that: In WSL1, both Windows & Linux were running on same machine. In WSL2, they are running in “separate” machines. The P9 server facilitates Windows <-> Linux file sharing. - In the scenario above, P9 allows Linux VM access to windows file share
- 9P facilitates \\WSL$ share
- P9 here facilitates mounting of windows file share
- Single linux kernel serves multiple distros