# ls $(guix build nss-certs)/etc
accepted connection from pid 15, user root
0.2 MB will be downloaded:
   /gnu/store/ajjnwdd57q3m4hv4xv7wp91nyy0j4li7-nss-certs-3.34.1
@ substituter-started /gnu/store/ajjnwdd57q3m4hv4xv7wp91nyy0j4li7-nss-certs-3.34.1 /gnu/store/pii5cimi72lj5l7793h54g5sg0sr2apl-guix-0.14.0/libexec/guix/substitute
Downloading https://mirror.hydra.gnu.org/guix/nar/gzip/ajjnwdd57q3m4hv4xv7wp91nyy0j4li7-nss-certs-3.34.1...
 nss-certs-3.34.1  150KiB            2.6MiB/s 00:00 [##################] 100.0%

@ substituter-failed /gnu/store/ajjnwdd57q3m4hv4xv7wp91nyy0j4li7-nss-certs-3.34.1 0 hash mismatch in downloaded path `/gnu/store/ajjnwdd57q3m4hv4xv7wp91nyy0j4li7-nss-certs-3.34.1'
  expected: 9a66ef45323f83e4070be7351fbeb5fb51a451dbfd8dca5ed5f795502913beef
  actual:   eea654bfb7fa51394e15331d95b590d801425744146c3cd6b10d2fa30be915f0
guix build: error: build failed: some substitutes for the outputs of derivation `/gnu/store/xh6rwmiw24nn9fq9vz31l6d6nbkp37i0-nss-certs-3.34.1.drv' failed (usually happens due to networking issues); try `--fallback' to build derivation from source