rsmemsiz: 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/rsmemsiz - from package: ax25-tools

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