xclip: 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/xclip - from package: xclip

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

On Debian possible default full paths are:

/usr/bin/xclip - from package: xclip

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

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