instmodsh: 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/instmodsh - from package: perl-ExtUtils-MakeMaker

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

On Debian possible default full paths are:

/usr/bin/instmodsh - from package: perl

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

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