pure-ftpd: (?@?) [ERROR] Sorry, but that file doesn't exist: [/etc/ssl/private/pure-ftpd.pem]

Written by Claudio Kuenzler - 0 comments

Published on July 30th 2024 - Listed in Linux TLS Security

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A weird error was seen today when a TLS certificate needed to be replaced on a FTP server using pure-ftpd.

Once the certificate file (by default /etc/ssl/private/pure-ftpd.pem) was replaced with the new content (it's actually a bundle of private key + certificate), the following error showed up after pure-ftpd was restarted:

root@ftp:~# systemctl status pure-ftpd
- pure-ftpd.service
     Loaded: loaded (/etc/init.d/pure-ftpd; generated)
     Active: active (exited) since Tue 2024-07-30 12:34:31 CEST; 4s ago
       Docs: man:systemd-sysv-generator(8)
    Process: 2164432 ExecStart=/etc/init.d/pure-ftpd start (code=exited, status=0/SUCCESS)
        CPU: 43ms

Jul 30 12:34:31 ftp systemd[1]: Starting pure-ftpd.service...
Jul 30 12:34:31 ftp pure-ftpd[2164432]: Starting ftp server:
Jul 30 12:34:31 ftp pure-ftpd[2164440]: Running: /usr/sbin/pure-ftpd -l puredb:/etc/pure-ftpd/pureftpd.pdb -l pam -A -O clf:/var/log/pure-ftpd/transfer.log -J HIGH:ME>
Jul 30 12:34:31 ftp systemd[1]: Started pure-ftpd.service.
Jul 30 12:34:31 ftp pure-ftpd[2164441]: (?@?) [ERROR] Sorry, but that file doesn't exist: [/etc/ssl/private/pure-ftpd.pem]

By reading this error, it looks like a typical permission problem. However the documentation (README.TLS) confirms that chmod 600 should be set on this file:

mkdir -p /etc/ssl/private
openssl dhparam -out /etc/ssl/private/pure-ftpd-dhparams.pem 2048
openssl req -x509 -nodes -newkey rsa:2048 -sha256 -keyout \
  /etc/ssl/private/pure-ftpd.pem \
  -out /etc/ssl/private/pure-ftpd.pem
chmod 600 /etc/ssl/private/*.pem

And the file does indeed exist:

root@ftp:~# cat /etc/ssl/private/pure-ftpd.pem
-----BEGIN PRIVATE KEY-----
[...]
-----END PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
[...]
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
[...]
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
[...]
-----END CERTIFICATE-----

After a lot of research, which led to no real hint, it turned out to be a copy+paste error.

The certificates (server certificate, intermediate certificate and root ca certificate) were copied from a Confluence page into the file on the Linux server (pasted using vim). This somehow added weird characters or spaces, leading to an invalid (internal) verification. The error, that the file doesn't exist, is therefore misleading.

Once the key+certificates bundle was properly created on a Linux system and then copied from the command line, everything turned out to be good.

$ cat private.key server.crt ica.pem rootca.crt > pure-ftpd.pem

Once this was placed on the FTP server and pure-ftpd restarted, no error anymore:

root@ftp:~# systemctl status pure-ftpd
- pure-ftpd.service
     Loaded: loaded (/etc/init.d/pure-ftpd; generated)
     Active: active (running) since Tue 2024-07-30 12:39:17 CEST; 1s ago
       Docs: man:systemd-sysv-generator(8)
    Process: 2167138 ExecStart=/etc/init.d/pure-ftpd start (code=exited, status=0/SUCCESS)
      Tasks: 1 (limit: 9434)
     Memory: 2.0M
        CPU: 41ms
     CGroup: /system.slice/pure-ftpd.service
             |-2167148 "pure-ftpd (SERVER)

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