brew install mosquito

Devoluciones:

 Warning: mosquitto 1.6.8 is already installed, it's just not linked
You can use `brew link mosquitto` to link this version.

Intento de enlace:

 Users-MacBook-Air:~ user$ brew link mosquitto
Linking /usr/local/Cellar/mosquitto/1.6.8... 
Error: Could not symlink sbin/mosquitto
/usr/local/sbin is not writable.
Users-MacBook-Air:~ user$ ls /usr/local/sbin
ls: /usr/local/sbin: No such file or directory
Users-MacBook-Air:~ user$ sudo brew link mosquitto
Password:
Error: Running Homebrew as root is extremely dangerous and no longer supported.
As Homebrew does not drop privileges on installation you would be giving all
build scripts full access to your system.
Users-MacBook-Air:~ user$ mkdir /usr/local/sbin
mkdir: /usr/local/sbin: Permission denied

El objetivo es invocar mosquitto_sub . ¿Qué se debe hacer para habilitar mosquito_sub?

 Users-MacBook-Air:~ user$ brew upgrade mosquito
Warning: mosquitto 1.6.8 already installed
Users-MacBook-Air:~ user$ mosquitto_sub -h test.mosquitto.org -t "#" -v
-bash: mosquitto_sub: command not found

ACTUALIZACIONES \ RESPUESTAS

CREAR DIRECTORIO: sudo mkdir /usr/local/sbin

 Users-MacBook-Air:~ user$ mosquitto_sub -h test.mosquitto.org -t "#" -v
-bash: mosquitto_sub: command not found
Users-MacBook-Air:~ user$ sudo mkdir /usr/local/sbin
Password:
Users-MacBook-Air:~ user$ ls -l  /usr/local/ |  grep sbin
drwxr-xr-x    2 root  wheel     64 Dec 15 14:00 sbin
Users-MacBook-Air:~ user$ ls -l  /usr/local/sbin
Users-MacBook-Air:~ user$ chmod 777 /usr/local/sbin
chmod: Unable to change file mode on /usr/local/sbin: Operation not permitted
Users-MacBook-Air:~ user$ sudo chmod 777 /usr/local/sbin
Users-MacBook-Air:~ user$ ls -l  /usr/local/ |  grep sbin
drwxrwxrwx    2 root  wheel     64 Dec 15 14:00 sbin
Users-MacBook-Air:~ user$ brew link mosquitto
Linking /usr/local/Cellar/mosquitto/1.6.8... 30 symlinks created
Users-MacBook-Air:~ user$ mosquitto_sub -h test.mosquitto.org -t "#" -v
owntracks/busware/iPhone {"t":"t","tst":1576424485,"acc":65,"_type":"location","alt":17,"lon":10.67649557998085,"vac":10,"lat":54.04553

Users-MacBook-Air:~ user$ sudo chmod 755 /usr/local/sbin
Password:
Users-MacBook-Air:~ user$ ls -l  /usr/local/ |  grep sbin
drwxr-xr-x    3 root  wheel     96 Dec 15 14:02 sbin

PRUEBA DE MODIFICACIÓN DE RUTA

 Users-MacBook-Air:~ user$ echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
Users-MacBook-Air:~ user$ PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/Cellar/mosquitto/ 
Users-MacBook-Air:~ user$ echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/Cellar/mosquitto/
Users-MacBook-Air:~ user$ mosquitto_sub -h test.mosquitto.org -t "#" -v
-bash: mosquitto_sub: command not found