14.04 - mona is not in the sudoers file. This incident will be reported - Ask Ubuntu

so did sudo apt-get upgrade , said y question asked me , not sudoer anymore. our root isn't sudoer anymore. what's solution?

configuration file '/etc/sudoers'  ==> modified (by or script) since installation.  ==> package distributor has shipped updated version.    ?  options are:     y or  : install package maintainer's version     n or o  : keep currently-installed version       d     : show differences between versions       z     : start shell examine situation  default action keep current version. *** sudoers (y/i/n/o/d/z) [default=n] ? y installing new version of config file /etc/sudoers ... setting apt-transport-https (1.0.1ubuntu2.15) ... setting libisc95 (1:9.9.5.dfsg-3ubuntu0.10) ... setting libdns100 (1:9.9.5.dfsg-3ubuntu0.10) ... setting libisccc90 (1:9.9.5.dfsg-3ubuntu0.10) ... setting libisccfg90 (1:9.9.5.dfsg-3ubuntu0.10) ... setting libbind9-90 (1:9.9.5.dfsg-3ubuntu0.10) ... setting liblwres90 (1:9.9.5.dfsg-3ubuntu0.10) ... setting bind9-host (1:9.9.5.dfsg-3ubuntu0.10) ... setting dnsutils (1:9.9.5.dfsg-3ubuntu0.10) ... setting dbus (1.6.18-0ubuntu4.4) ... installing new version of config file /etc/dbus-1/system.conf ... setting python3-update-manager (1:0.196.22) ... setting update-manager-core (1:0.196.22) ... setting bazel (0.4.0) ... setting cuda-repo-ubuntu1404 (8.0.44-1) ... ok setting dbus-x11 (1.6.18-0ubuntu4.4) ... setting dkms (2.2.0.3-1.1ubuntu5.14.04.9) ... setting firefox (49.0.2+build2-0ubuntu0.14.04.1) ... please restart running instances of firefox, or experience problems. setting libxnvctrl0 (361.93.02-0ubuntu1) ... setting linux-generic-lts-saucy (3.13.0.100.108) ... setting linux-headers-generic-lts-saucy (3.13.0.100.108) ... setting linux-image-generic-lts-saucy (3.13.0.100.108) ... setting linux-libc-dev:amd64 (3.13.0-100.147) ... setting linux-tools-common (3.13.0-100.147) ... setting python-pil (2.3.0-1ubuntu3.3) ... setting python-imaging (2.3.0-1ubuntu3.3) ... processing triggers libc-bin (2.19-0ubuntu6.9) ... mona@pascal:~/computer_vision/deep_learning/ssd/caffe$ sudo apt-get install build-essential cmake git pkg-config mona not in sudoers file.  incident reported.   mona@pascal:~$ pwd /home/mona mona@pascal:~$ su - password:  su: authentication failure   mona@pascal:~$ sudo passwd root [sudo] password mona:  mona not in sudoers file.  incident reported. 

update: in grub, selected advanced options , recovery mode -> root , changed password using passwd mona , set passwd still doesn't let me sudo after rebooting! please suggest solutions.

mona@pascal:~$ su - password:  su: authentication failure 

the usual way give sudo rights account in ubuntu add admin and/or sudo groups, given sudo rights default.

if want modify sudoers configuration, should not edit /etc/sudoers directly, add local configuration in separate file in directory /etc/sudoers.d described in man sudoers. avoid problem experienced: since changes not in /etc/sudoers, can safely upgrade newer versions without losing configuration.

in order modify system files if sudo won't work, can go through recovery mode. can then, example, add mona sudo group with

usermod -ag sudo mona