icewm-session: 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/icewm-session - from package: icewm

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

On Debian possible default full paths are:

/usr/bin/icewm-session - from package: icewm

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

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