amstex: 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/bin/amstex - from package: texlive

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

On Debian possible default full paths are:

/usr/bin/amstex - from package: texlive-math-extra

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

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