---
name: "nix-env-set-flag"
section: "1"
platform: "linux"
package: "nix-bin"
version: "2.26.3+dfsg-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nix-env-set-flag"
---

# nix-env-set-flag(1)

modify meta attributes of installed packages

## Name

`nix-env --set-flag` - modify meta attributes of installed packages

## Synopsis

`nix-env` `--set-flag` *name* *value* *drvnames*

## Description

The `--set-flag` operation allows meta attributes of installed packages to be modified. There are several attributes that can be usefully modified, because they affect the behaviour of `nix-env` or the user environment build script:

- •

  `priority` can be changed to resolve filename clashes. The user environment build script uses the `meta.priority` attribute of derivations to resolve filename collisions between packages. Lower priority values denote a higher priority. For instance, the GCC wrapper package and the Binutils package in Nixpkgs both have a file `bin/ld`, so previously if you tried to install both you would get a collision. Now, on the other hand, the GCC wrapper declares a higher priority than Binutils, so the former’s `bin/ld` is symlinked in the user environment.

- •

  `keep` can be set to `true` to prevent the package from being upgraded or replaced. This is useful if you want to hang on to an older version of a package.

- •

  `active` can be set to `false` to “disable” the package. That is, no symlinks will be generated to the files of the package, but it remains part of the profile (so it won’t be garbage-collected). It can be set back to `true` to re-enable the package.

{{#include ./opt-common.md}}

{{#include ../opt-common.md}}

{{#include ../env-common.md}}

## Examples

To prevent the currently installed Firefox from being upgraded:

```
$ nix-env --set-flag keep true firefox
```

After this, `nix-env --upgrade` will ignore Firefox.

To disable the currently installed Firefox, then install a new Firefox while the old remains part of the profile:

```
$ nix-env --query
firefox-2.0.0.9 (the current one)
$ nix-env --preserve-installed --install firefox-2.0.0.11
installing `firefox-2.0.0.11'
building path(s) `/nix/store/myy0y59q3ig70dgq37jqwg1j0rsapzsl-user-environment'
collision between `/nix/store/...-firefox-2.0.0.11/bin/firefox'
  and `/nix/store/...-firefox-2.0.0.9/bin/firefox'.
(i.e., can’t have two active at the same time)
$ nix-env --set-flag active false firefox
setting flag on `firefox-2.0.0.9'
$ nix-env --preserve-installed --install firefox-2.0.0.11
installing `firefox-2.0.0.11'
$ nix-env --query
firefox-2.0.0.11 (the enabled one)
firefox-2.0.0.9 (the disabled one)
```

To make files from `binutils` take precedence over files from `gcc`:

```
$ nix-env --set-flag priority 5 binutils
$ nix-env --set-flag priority 10 gcc
```