thinkfan: command not found

Have You tried accessing the binary with the full path?

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 Debian possible default full paths are:

/usr/sbin/thinkfan - from package: thinkfan

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