How to get real root permissions on OS X

Question

I'm a noob with OSX (10.8.5) wanting to install homebrew on an Airbook.

Installing homebrew fails straight away because it can't mkdir /usr/local. So I try with sudo - same problem. Trying sudo mkdir /usr/local directly also fails of course.

My user 'mjb' has admin rights (well according to the Users/Groups GUI interface) but I can't figure out how to do anything useful !

As my 'admin' user mjb, typing id shows "uid=502(mjb) gid=20(staff) ...." typing sudo id shows "uid=503(root) gid=1000 ...."

I've searched and all the solutions I see involve editing some file (root.plist) directly or using visudo ... and of course I don't have the permissions to do that !

I just want "real" sudo access so I can install stuff on the command-line (boot2docker).

Thanks for any suggestions

Update:

dscl . ls /Users provides a lot of output:

_amavisd
_appleevents
_appowner
_appserver
_ard
_assetcache
_atsserver
_avbdeviced
_calendar
_ces
_clamav
_coreaudiod
_cvmsroot
_cvs
_cyrus
_devdocs
_devicemgr
_dovecot
_dovenull
_dpaudio
_eppc
_ftp
_geod
_installassistant
_installer
_jabber
_kadmin_admin
_kadmin_changepw
_krb_anonymous
_krb_changepw
_krb_kadmin
_krb_kerberos
_krb_krbtgt
_krbtgt
_lda
_locationd
_lp
_mailman
_mcxalr
_mdnsresponder
_mysql
_netbios
_netstatistics
_networkd
_postfix
_postgres
_qtss
_sandbox
_screensaver
_scsd
_securityagent
_serialnumberd
_softwareupdate
_spotlight
_sshd
_svn
_taskgated
_teamsserver
_timezone
_tokend
_trustevaluationagent
_unknown
_update_sharing
_usbmuxd
_uucp
_warmd
_webauthserver
_windowserver
_www
daemon
mjb
nobody
Paulina
root

dscl . read /Users/root

AppleMetaNodeLocation: /Local/Default
GeneratedUID: FFFFEEEE-DDDD-CCCC-BBBB-AAAA00000000
NFSHomeDirectory: /Local/Users/root
Password: *
PasswordPolicyOptions: <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "apple.com/DTDs/PropertyList-1.0.dtd">; 
<plist version="1.0">
<dict>
    <key>failedLoginCount</key>
    <integer>0</integer>
    <key>failedLoginTimestamp</key>
    <date>2001-01-01T00:00:00Z</date>
    <key>lastLoginTimestamp</key>
    <date>2001-01-01T00:00:00Z</date>
    <key>passwordLastSetTime</key> 
    <date>2015-06-09T18:48:49Z</date>
</dict>
</plist>
PrimaryGroupID: 1000
RealName:
 Mike Bright
RecordName:
 root
 BUILTIN\Local System
RecordType: dsRecTypeStandard:Users 
SMBSID: S-1-5-18 
UniqueID: 503 
UserShell: /bin/bash

Answer 1

The real superuser root account is always Always ALWAYS UID 0. How you got an account named "root" on your system with UID 503 is beyond me.

You may need to manually fix up your Directory Services data store (your users and groups database) with Directory Utility or dscl.

open /System/Library/CoreServices/Directory\ Utility.app

I think that was the path back in 10.8.5, but it's been a long time. Nowadays it's…

open /System/Library/CoreServices/Applications/Directory\ Utility.app

That app has a Directory Editor you should be able to use to see what's going on with the inner details of the accounts on your machine.

Alternatively, seeing the output of the following two commands would help me see what's going on:

dscl . ls /Users
dscl . read /Users/root