If you fall in a nasty situation where a file in the Nix store is corrupted, you can recover it by using the nix-store command. The nix-store command has a --repair option that can be used to recover corrupted files, and a --check-contents option to verify the integrity of the Nix store.
You can fall in such situation if you alter manually a file, or you have a hardware failure that corrupts the file.
[root@nixos:~]# nix-store --verify --repair --check-contents
reading the Nix store...
checking path existence...
checking link hashes...
checking store hashes...
path '/nix/store/0db33kxbw5k0lbwrkc037dbqyz3rgzw8-libnftnl-1.2.6' was modified! expected hash 'sha256:0nhmj43w3i1qkq4p87s0w03fl16f0gwq7yi6k22hb3ljdf2r8wcz', got 'sha256:0sjjj9z1dhilhpc8pq4154czrb79z9cm044jvn75kxcjv6v5l2m5'
copying path '/nix/store/0db33kxbw5k0lbwrkc037dbqyz3rgzw8-libnftnl-1.2.6' from 'https://cache.nixos.org'...
path '/nix/store/0iixl4gy02ci4n9d9f7cs6abb1y6nffp-nixos-24.05pre598085.c75037bbf909' was modified! expected hash 'sha256:0c7x36xjl96l0rvqja2rp5v7nfmwm0fcbzgc035443aai4ssbzaj', got 'sha256:07v4kynvhsyi8imahiwf1w4vkpis3sw8zffly5jmn4674f36nizw'
copying path '/nix/store/0iixl4gy02ci4n9d9f7cs6abb1y6nffp-nixos-24.05pre598085.c75037bbf909' from 'https://cache.nixos.org'...
path '/nix/store/46dac1q1v9yp7dfanyyginpk8z7zvnf5-etc-fstab' was modified! expected hash 'sha256:1y4qhsizjlllgzjsnd8sfnj55akp8lq8zbsy2d8vq8z4r54irsm7', got 'sha256:14pw1n0yyzf6jqdql1lcn222g9gv8g0f91gmissb651vblgwdcjc'
checking path '/nix/store/46dac1q1v9yp7dfanyyginpk8z7zvnf5-etc-fstab'...
path '/nix/store/46dac1q1v9yp7dfanyyginpk8z7zvnf5-etc-fstab' is corrupted or missing!
checking path '/nix/store/xz6h70zgmd6wf2931rdg5v4khnsxfg40-bash-5.2p26'...
checking path '/nix/store/z0yj0l3k9bdvvnp5iabmri4cbpkrwdpq-stdenv-linux'...
copying path '/nix/store/xz6h70zgmd6wf2931rdg5v4khnsxfg40-bash-5.2p26' from 'https://cache.nixos.org'...
checking path '/nix/store/5sdcqrw3rjzc8ddndsnbbla0mfp2wygr-libidn2-2.3.7'...
...
checking path '/nix/store/sdrzrynbirmgk47byj2k9280zhh268v6-xgcc-13.2.0-libgcc'...
copying path '/nix/store/z0yj0l3k9bdvvnp5iabmri4cbpkrwdpq-stdenv-linux' from 'https://cache.nixos.org'...
checking path '/nix/store/1639yfqw64vivi4163ljawq8w8raypvj-file-5.45'...
checking path '/nix/store/18qib5wgasqrrp49lyjj0majydlnmpzh-gnu-config-2023-09-19'...
checking path '/nix/store/2shf6zxxx9a5mjskhhc2g55adxrxblhr-ed-1.20.1'...
...
checking path '/nix/store/y650rhxwi5ry2v33ns8wcc1c722v1h0w-gmp-with-cxx-6.3.0'...
checking path '/nix/store/z7abiwmqsg4m7d877sq1dinbxxsgg5jr-patchelf-0.15.0'...
repairing outputs of '/nix/store/x4hbrz2649pi0bj8vy5ym13fyg84n7m1-etc-fstab.drv'...
path '/nix/store/m2ffzbr042hj16fbbb2ngbgzw06bkgx4-libnetfilter_conntrack-1.0.9' was modified! expected hash 'sha256:1qrcrjdd7qzdv8bwcig38bg4nzsbnw61ns0gy7azrkighiydxax0', got 'sha256:0vaig2vwqgl9mx9kkv6awbzcmi46gcbxid7pgz31bjqckm1i3553'
copying path '/nix/store/m2ffzbr042hj16fbbb2ngbgzw06bkgx4-libnetfilter_conntrack-1.0.9' from 'https://cache.nixos.org'...
path '/nix/store/wiyax30lh6wj0n04i2agpk1k8hmjg3zw-libnl-3.8.0' was modified! expected hash 'sha256:0chmfxb3rx5nmrskiwmp839hfq9g1qpy9jhhnnpv42l60bx9dkwz', got 'sha256:0sjjj9z1dhilhpc8pq4154czrb79z9cm044jvn75kxcjv6v5l2m5'
copying path '/nix/store/wiyax30lh6wj0n04i2agpk1k8hmjg3zw-libnl-3.8.0' from 'https://cache.nixos.org'...
If this command finish to run successfully, you recovered.