Digite no terminal como root:
nano /etc/sudoers e veja se está com esta configuração, se não altere e reinicie o servidor.
Obs: usuário é o seu nome de usuário que aparece no prompt do terminal.
# /etc/sudoers
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the man page for details on how to write a sudoers file.
#
Defaults env_reset
# Host alias specification
# User alias specification
# Cmnd alias specification
# User privilege specification
root ALL=(ALL) ALL
# Uncomment to allow members of group sudo to not need a password
# (Note that later entries override this, so you might need to move
# it further down)
# %sudo ALL=NOPASSWD: ALL
# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL
usuario ALL=NOPASSWD:/usr/bin/lanbr
usuario ALL=NOPASSWD:/usr/bin/xlanbr
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