jstack: 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/lib/debug/usr/lib/jvm/java-7-openjdk-amd64/bin/jstack - from package: openjdk-7-dbg
/usr/lib/jvm/java-7-openjdk-amd64/bin/jstack - from package: openjdk-7-jdk

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

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