Mounts

Week 0x8 I

Prof. Calvin

Crypto

Announcements

• Welcome to variously CS 276/CS 540
  • Back to containers.
  • Week off from C
  • Two lectures with exercises
• Action Items:
  • Basedterm ✔️
  • BigRSA due 31 Mar

Today

• The file system
• Linux and even… WINDOWS development????
  • Has science gone too far
• Symbolic Linkages
• Containers but good

Motivation

Motivation

Motivation

In brief

• I am often on a Linux partition when a non-technical PM attempts to reach me through MS Suite
  • I can run MS Suite on Linux which, uh, defeats to purpose of being on Linux

In brief

• I am often on a Windows partition when I get questions like:
  • Can I fix this compatibility issue with whitespace line termination?
  • Will this run on Win and *nix?
  • Can you take a quick md5sum of this file?
• Often I just need to run a quick script or executable on files in a Windows file system using Linux syscalls.

Separate Problem

1. vim mywork.c
2. podman build -t tester . # COPY mywork.c
3. podman run tester python3 tester.py
4. I get negative one billion points
5. vim mywork.c
6. podman run tester python3 tester.py still gives negative on billion because the file systems are desynced.

Bind Mounts

When you use a bind mount, a file or directory on the host machine is mounted from the host into a container. By contrast, when you use a volume, a new directory is created within Docker’s storage directory on the host machine, and Docker manages that directory’s contents.

Let’s step through the process

• I make a container image that I’m relatively happy with.
  • Save this in a containerfile
  • Build it and have it live under the local podman images container repository.
  • Or… push to GHCR? Hmmm?
    • Soon™️

Container image

• I rarely use utilities other than these few.

Containerfile

FROM ubuntu 

RUN apt update && apt install gcc vim python3 astyle -y

Astyle

• astyle might be new to you
• It completely rules
• It’s old, new one is Clang-Tidy
• Requires LLVM back-end which is…
• For the Rust class
• Also coc usually via npm and (gags) neovim

Sample

$ cat octal.c
#include <stdio.h>
int main(){printf("%o\n",10);/* hm */return/* blah */ 0;}
$ gcc octal.c
$ ./a.out
12
$ astyle octal.c
Formatted  /home/user/tmp/octal.c
$ cat octal.c
#include <stdio.h>
int main() {
    printf("%o\n",10);/* hm */return/* blah */ 0;
}
$ gcc octal.c
$ ./a.out
12

Hightlight

• vim octal.c

before

#include <stdio.h>
int main(){printf("%o\n",10);/* hm */return/* blah */ 0;}

• astyle octal.c

astyle

#include <stdio.h>
int main() {
    printf("%o\n",10);/* hm */return/* blah */ 0;
}

• Learn more astyle -h (I’ve never read it).

Style Guides

• The people that taught me C wrote this
• The iconic living legend Linux kernel hackers, who are never wrong, wrote this
• I’m not up-to-date on Google C but Google C++ is here
  • Our “header” instruction is from their “The #define Guard” heading.

Anyways

• To my knowledge this is all I’ve used this term outside of one-offs for testing.

gcc \
vim \
python3 \
astyle

• Though can probably manage gcc only after today.

Let’s step through the process

• I make a container image that I’m relatively happy with.
  • vim Containerfile
  • podman build -t crypto .
• Now, just spin up a transient container when I need anything.

Run options

• Two competing idealogues
  • I am on docker documentation not podman
  • podman I think assumes you know what you are doing (I don’t)
• Mount

docker run --mount type=bind,src=<host-path>,dst=<container-path>

• Volume

docker run --volume <host-path>:<container-path>

Quote Docker

In general, --mount is preferred. The main difference is that the --mount flag is more explicit and supports all the available options.

• Volume is basically being gradually depreciated.
• Volumes are in general podman/docker managed and…
  • We don’t trust code other people wrote.
  • Or code we wrote.

Sample

• https://github.com/cd-c89/crypto/blob/main/podman/podman.sh

podman run --mount type=bind,src=$PWD/..,target=/mnt -d -t crypto /bin/bash

Breakdown

Arg	Meaning
podman	container command
run	start a container from some image
–mount	let container see files that live outside container

Breakdown

Arg	Meaning
type=bind	the files will be the same in a host folder and container folder
src=	This is the folder on the host
$PWD/..	This is the file above the current working directory

Try it

• $PWD is a shell built-in like $?

$ echo $PWD
/home/user
$ pwd
/home/user

• Can use it in scripts.

$ ls $PWD/..
user
$ ls ..
user

Sample

• Make the .. directory on host be visible to container.

podman run --mount type=bind,src=$PWD/..,target=/mnt -d -t crypto /bin/bash

Breakdown

Arg	Meaning
target=	This is the folder on the container
/mnt	That is the mnt (mount) directory under root /
-d	Start the container detached

• I couldn’t get this to work attached (on Windows) but didn’t try very hard.
  • On Linux everything is easy (always)

Breakdown

Arg	Meaning
-t	What should the name (tag) be of Container image?
crypto	The tag I used during podman build
/bin/bash	The executable to run within the container

Sample

podman run --mount type=bind,src=$PWD/..,target=/mnt -d -t crypto /bin/bash

1. Start a shell
2. In a container of the image based on the Containerfile
3. Where /mnt refers to files on the host machine

See it

user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto/podman$ /bin/bash podman.sh
c25d7d0db5d60efca7c1140dd9b8217a27e511caa4f5a5fdf2fc21e90ad45f17
user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto/podman$ ls ..
4096_t  README.md  enigma  macros  ops_ui  podman  rsainc  shainc
user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto/podman$ podman exec -it c2 /bin/bash
root@c25d7d0db5d6:/# ls /mnt
4096_t  README.md  enigma  macros  ops_ui  podman  rsainc  shainc
root@c25d7d0db5d6:/#

More fun

• I have gcc inside that container.
• I can compile inside that container.
• Let’s step through an example.
• On my host, that is, not in container:

hi.c

#include <stdio.h>

int main() {
        printf("hi\n");
        return 0;
}

user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto/podman$ cd ..
user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto$ podman ps
CONTAINER ID  IMAGE                    COMMAND     CREATED        STATUS            PORTS       NAMES
c25d7d0db5d6  localhost/crypto:latest  /bin/bash   7 minutes ago  Up 7 minutes ago              determined_shockley
user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto$ vim hi.c
user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto$ cat hi.c
#include <stdio.h>

int main() {
        printf("hi\n");
        return 0;
}
user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto$ podman exec -it c2 cat /mnt/hi.c
#include <stdio.h>

int main() {
        printf("hi\n");
        return 0;
}

Compile

• I can compile within the Container
  • Just use exec (run command)
  • With gcc
  • With /mnt files

  user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto$ podman ps
  CONTAINER ID  IMAGE                    COMMAND     CREATED        STATUS            PORTS       NAMES
  c25d7d0db5d6  localhost/crypto:latest  /bin/bash   7 minutes ago  Up 7 minutes ago              determined_shockley
  podman exec -it c2 gcc /mnt/hi.c -o /mnt/hi.out

Run it

• Can run on the host device.
  • Well, making some pretty heavy assumptions.
  • This was ubuntu-to-ubuntu, after all

  user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto$ ./hi.out
  hi

• Can run in the container

user@DESKTOP-THMS2PJ:~/dev/crypto/repos/crypto$ podman exec -it c2 ./mnt/hi.out
hi

Ubuntu on Windows

• An astute learning will notice this means it no longer matters which OS your text editor runs under
• And here, in this class, we all love MS Windows.

It’s Popular

Windows Commands

• Windows has two command lines.
  • Don’t blame me I voted for Free and Open Source Software (FOSS)
  • So does Windows, now (hence WSL)

1. cmd.exe from DOS, which runs .bat files
2. PowerShell, for .NET, which runs .ps1 files

Why two shells?

• How does Windows work (pick one):
  • It doesn’t.
  • I don’t know.

Scripts

• For reference, here is my .sh script to mount folders:

podman.sh

podman run --mount type=bind,src=$PWD/..,target=/mnt -d -t crypto /bin/bash

• Here is how I run the same under the “Command” shell cmd.exe

windows.bat

podman run --mount type=bind,src=%cd%\..,target=/mnt -d -t crypto /bin/bash

One difference

• podman commands are the same on all OSes
• All commands within the container are the same, as the container is the same
• The only difference is the src
  • On Windows:
    • Paths are backslash vs. forward slash delineated
    • %cd% not$PWD` gives the current directory.

    windows.bat

    podman run --mount type=bind,src=%cd%\..,target=/mnt -d -t crypto /bin/bash

Windows Image

• Presumably I can refer to wsl images from the Windows host, I didn’t try.

C:\Users\cd-desk\Documents\dev\crypto\podman>podman machine start
Starting machine "podman-machine-default"
API forwarding for Docker API clients is not available due to the following startup failures.
        could not start api proxy since expected pipe is not available: podman-machine-default

Podman clients are still able to connect.
Machine "podman-machine-default" started successfully

C:\Users\cd-desk\Documents\dev\crypto\podman>podman build -t crypto .

Launch Container

C:\Users\cd-desk\Documents\dev\crypto\podman>.\window.bat

C:\Users\cd-desk\Documents\dev\crypto\podman>podman run --mount type=bind,src=C:\Users\cd-desk\Documents\dev\crypto\podman\..,target=/mnt -d -t crypto /bin/bash
9a1b0fb2a8f87d3639149ee41fb2dcb822f5a7cbd971a39cdc77150a79774765

C:\Users\cd-desk\Documents\dev\crypto\podman>

vim

• I of course also have vim installed on Windows, but I don’t know when I did that or how.

C:\Users\cd-desk\Documents\dev\crypto>vim hi.c

C:\Users\cd-desk\Documents\dev\crypto>type hi.c
#include <stdio.h>

int main() {
        printf("i wrote this on windows lol meow\n");
        return 0;
}

C:\Users\cd-desk\Documents\dev\crypto>

Compile

C:\Users\cd-desk\Documents\dev\crypto>podman exec -it 9a gcc /mnt/hi.c -o /mnt/hi.out

C:\Users\cd-desk\Documents\dev\crypto>dir hi.out
 Volume in drive C has no label.
 Volume Serial Number is 5CEC-43F9

 Directory of C:\Users\cd-desk\Documents\dev\crypto

03/12/2025  05:33 PM            15,960 hi.out
               1 File(s)         15,960 bytes
               0 Dir(s)  99,378,515,968 bytes free

C:\Users\cd-desk\Documents\dev\crypto>

Run

C:\Users\cd-desk\Documents\dev\crypto>podman exec -it 9a ./mnt/hi.out
i wrote this on windows lol meow

C:\Users\cd-desk\Documents\dev\crypto>

• Windows Development: It’s easy.

It’s not

• Windows opened a window asking me what to do when I tried to run this.

C:\Users\cd-desk\Documents\dev\crypto>.\hi.out

C:\Users\cd-desk\Documents\dev\crypto>

Exercise

• Windows users:
  • Get this to run in PowerShell
• Mac users:
  • Get this to run on Mac, the .sh should mostly work. Right?
• Linux users:
  • Develop a “portable” binary that works across distributions.

Announcements

• Welcome to variously CS 276/CS 540
  • Back to containers.
  • Week off from C
  • Two lectures with exercises
• Action Items:
  • BigRSA due 31 Mar