unhide-tcp: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/unhide-tcp - from package: unhide

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/unhide-tcp - from package: unhide

You may install the required package with command apt-get install {package}

Error in other languages:
unhide-tcp: bevel nie gevind nie
unhide-tcp: comandă negăsită
unhide-tcp: comando não encontrado
unhide-tcp: commande introuvable
unhide-tcp: command not found
unhide-tcp: käsku ei ole
unhide-tcp: không tìm thấy lệnh
unhide-tcp: komanda nerasta
unhide-tcp: Kommando nicht gefunden.
unhide-tcp: kommandot finns inte
unhide-tcp: komut yok
unhide-tcp: nie znaleziono polecenia
unhide-tcp: níor aimsíodh an t-ordú
unhide-tcp: no se encontró la orden
unhide-tcp: no s'ha trobat l'ordre
unhide-tcp: opdracht niet gevonden
unhide-tcp: parancs nem található
unhide-tcp: perintah tidak ditemukan
unhide-tcp: príkaz nenájdený
unhide-tcp: příkaz nenalezen
unhide-tcp: команда не найдена
unhide-tcp: командата не е открита
unhide-tcp: 命令找不到
unhide-tcp: コマンドが見つかりません