tkremind: 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 Debian possible default full paths are:

/usr/bin/tkremind - from package: tkremind

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

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