sshmitm: 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/sshmitm - from package: dsniff

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

On Debian possible default full paths are:

/usr/sbin/sshmitm - from package: dsniff

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

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