Using powershell to restart computers if -LastBootupTime = -gt 10 days - database

Question

I'm trying to make a script that checks how long the computers on a network are on, and if they are on for more then 10 days they need to restart. I'm planning to run the script automatically with task manager every Sunday.
Thanks to #vonPryz I've got something like this now:
$clients = get-content "C:\Documents\lijstcomputers.txt"
foreach ($client in $clients) {
if (test-connection -computername $client -BufferSize 16 -Count 1 -Quiet) {
write-Host $client is online
$uptime = (get-date) - (gcim Win32_OperatingSystem -computer $client).LastBootUpTime
$startTime = [Management.ManagementDateTimeConverter]::ToDateTime((gwmi Win32_OperatingSystem -computer $client).lastbootuptime)
if( $uptime.days -ge 10) {
restart-computer -computername $client
add-content -path "c:\path\to\log.txt" -value "$client, $startTime, $uptime"
}
}
else {
write-Host $client is offline
}
}
But now I'm getting this error:
gcim : WinRM cannot complete the operation. Verify that the specified computer name is valid, that the computer is accessible over the network, and
that a firewall exception for the WinRM service is enabled and allows access from this computer. By default, the WinRM firewall exception for publ
ic profiles limits access to remote computers within the same local subnet.
At line:1 char:25
+ $uptime = (get-date) - (gcim Win32_OperatingSystem -computer $client).LastBootUp ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ConnectionError: (root\cimv2:Win32_OperatingSystem:String) [Get-CimInstance], CimException
+ FullyQualifiedErrorId : HRESULT 0x80338126,Microsoft.Management.Infrastructure.CimCmdlets.GetCimInstanceCommand
+ PSComputerName : ASND0042
Cannot find an overload for "op_Subtraction" and the argument count: "2".
At line:1 char:1
+ $uptime = (get-date) - (gcim Win32_OperatingSystem -computer $client).LastBootUp ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodException
+ FullyQualifiedErrorId : MethodCountCouldNotFindBest

Answer 1

Since you already got some parts covered, this isn't just a plz give me teh codez and thus warrants help. So let's outline how the whole script should look.
# Write computer names into a file, one per row for easier management
$clients = get-content "c:\ListOfComputers.txt"
foreach ($client in $clients) {
# If computer's not up, there's no need to check uptime
if (test-connection -computername $client -BufferSize 16 -Count 1 -Quiet) {
write-Host $client is online
# Get uptime
$uptime = (get-date) - (gcim Win32_OperatingSystem -computer $client).LastBootUpTime
# Get start time
$startTime = [Management.ManagementDateTimeConverter]::ToDateTime((gwmi Win32_OperatingSystem -computer $client).lastbootuptime)
# Restart the client if uptime's at least 10 days.
if( $uptime.days -ge 10) {
restart-computer -computername $client
# Add client name, start date and uptime into a log file
add-content -path "c:\path\to\log.txt" -value "$client, $startTime, $uptime"
}
}
else {
write-Host $client is offline
}
}
This skeleton can be further improved by adding some error handling and, say, proper CSV export.