peekfd: 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/peekfd - from package: psmisc

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

On Debian possible default full paths are:

/usr/bin/peekfd - from package: psmisc

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

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