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Nix, the purely functional package manager
435848cef1
I regularly pass around simple scripts by using nix-shell as the script
interpreter, eg. like this:
#!/usr/bin/env nix-shell
#!nix-shell -p dd_rescue coreutils bash -i bash
While this works most of the time, I recently had one occasion where it
would not and the above would result in the following:
$ sudo ./myscript.sh
bash: ./myscript.sh: No such file or directory
Note the "sudo" here, because this error only occurs if we're root.
The reason for the latter is because running Nix as root means that we
can directly access the store, which makes sure we use a filesystem
namespace to make the store writable. XXX - REWORD!
So when stracing the process, I stumbled on the following sequence:
openat(AT_FDCWD, "/proc/self/ns/mnt", O_RDONLY) = 3
unshare(CLONE_NEWNS) = 0
... later ...
getcwd("/the/real/cwd", 4096) = 14
setns(3, CLONE_NEWNS) = 0
getcwd("/", 4096) = 2
In the whole strace output there are no calls to chdir() whatsoever, so
I decided to look into the kernel source to see what else could change
directories and found this[1]:
/* Update the pwd and root */
set_fs_pwd(fs, &root);
set_fs_root(fs, &root);
The set_fs_pwd() call is roughly equivalent to a chdir() syscall and
this is called when the setns() syscall is invoked[2].
[1]:
|
||
|---|---|---|
| .github | ||
| config | ||
| contrib | ||
| doc/manual | ||
| m4 | ||
| maintainers | ||
| misc | ||
| mk | ||
| perl | ||
| scripts | ||
| src | ||
| tests | ||
| .dir-locals.el | ||
| .editorconfig | ||
| .gitignore | ||
| .version | ||
| boehmgc-coroutine-sp-fallback.diff | ||
| bootstrap.sh | ||
| configure.ac | ||
| COPYING | ||
| default.nix | ||
| docker.nix | ||
| flake.lock | ||
| flake.nix | ||
| local.mk | ||
| Makefile | ||
| Makefile.config.in | ||
| precompiled-headers.h | ||
| README.md | ||
| shell.nix | ||
Nix
Nix is a powerful package manager for Linux and other Unix systems that makes package management reliable and reproducible. Please refer to the Nix manual for more details.
Installation
On Linux and macOS the easiest way to install Nix is to run the following shell command (as a user other than root):
$ curl -L https://nixos.org/nix/install | sh
Information on additional installation methods is available on the Nix download page.
Building And Developing
See our Hacking guide in our manual for instruction on how to build nix from source with nix-build or how to get a development environment.
Additional Resources
- Nix manual
- Nix jobsets on hydra.nixos.org
- NixOS Discourse
- Matrix - #nix:nixos.org
- IRC - #nixos on libera.chat
License
Nix is released under the LGPL v2.1.