psselect: 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/psselect - from package: psutils

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

On Debian possible default full paths are:

/usr/bin/psselect - from package: psutils

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

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