Por que é '-o sec = krb5p' desnecessário no comando mount?

Question

Eu tenho um servidor nfs no Centos 7 com isso no arquivo / etc / exports:
/export *(rw,sec=krb5p)

Quando eu emito este comando, ele é montado com sucesso, como esperado:
mount -t nfs -o sec=krb5p server.example.com:/export /mnt/export

Ele também é montado com sucesso em resposta a este comando:
mount -t nfs server.example.com:/export /mnt/export

Em ambos os casos, a execução de findmnt mostra que a opção sec = krb5p está sendo usada. No segundo caso, existe um padrão oculto para o comando mount , ou o cliente se comunica com o servidor nfs e descobre que sec = krb5p é a única opção permitida?

    

Answer 1

RHEL / CentOS 7: o padrão é AUTH_SYS.

De documentação do RHEL 7 :

sec=mode
    Its default setting is sec=sys, which uses local UNIX UIDs and GIDs. These use
        AUTH_SYS to authenticate NFS operations."
    sec=krb5 uses Kerberos V5 instead of local UNIX UIDs and GIDs to 
        authenticate users.
    sec=krb5i uses Kerberos V5 for user authentication and performs integrity
        checking of NFS operations using secure checksums to prevent
        data tampering.
    sec=krb5p uses Kerberos V5 for user authentication, integrity checking,
        and encrypts NFS traffic to prevent traffic sniffing. This is the most
        secure setting, but it also involves the most performance overhead.

Ubuntu 16.04: Negociado.

De man nfs :

sec=flavor
    The security flavor to use for accessing files  on  this
    mount  point.   If the server does not support this fla‐
    vor, the mount operation fails.  If sec= is  not  speci‐
    fied, the client attempts to find a security flavor that
    both the client and the server supports.  Valid  flavors
    are  none,  sys,  krb5,  krb5i, and krb5p.  Refer to the
    SECURITY CONSIDERATIONS section for details.

OSX 10.12: Negociado.

De man mount_nfs :

sec=<mechanism>
    Force a specific security mechanism to be used for the mount,
    where mechanism is one of: krb5p, krb5i, krb5, or sys.  When this
    option is not given the security mechanism will be negotiated
    transparently with the remote server.