net_dropmonitor-report: 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/libexec/perf-core/scripts/python/bin/net_dropmonitor-report - from package: perf

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

On Debian possible default full paths are:

/usr/share/perf_3.16-core/scripts/python/bin/net_dropmonitor-report - from package: linux-tools-3.16

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

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