UNIX time for the first day of the month of last month

[jacortijo]

I am querying Nessus imported data and I would like to find old vulnerabilities still present today.
More precisely, events where the publication patch date (patchPubDate in UNIX time) is older than the first day of last month.

Example:     today is 9/11/2020 , so I would like to get the events older than 1/10/2020

I tried the query below but it gives 0 results which it is not possible because, unfortunately, I know I have dozens. So the query must be wrong somehow.  

note: last_found is when the vulnerability was seen for last time in UNIX time.

index=nessus sourcetype="tenable:sc:vuln" patchPubDate!=-1
| eval today = round(relative_time(now(), "-0d@d"))
| eval month = strftime(patchPubDate,"%m")
| eval lastmonth = month - 1
| eval year = strftime(patchPubDate,"%Y")
| eval dateLastMonth = "1/".lastmonth."/".year
| eval dateLastMonthUnix = strptime(dateLastMonth, "%d/%m/%Y")
| where last_found >= today AND pathPubDate<dateLastMonthUnix

any suggestion?

many thanks.

[somesoni2]

Are you sure? The relative_time syntax and value should work fine. 

Try running this run-anywhere search:

| makeresults | eval today=strftime( _time,"%F %T") | eval firstOfLastMonth=strftime( relative_time(_time,"-1mon@mon") ,"%F %T")

[richgalloway · Accepted solution]

There is a simpler way to get the first day of last month.  Use relative_time().

index=nessus sourcetype="tenable:sc:vuln" patchPubDate!=-1
| eval today = relative_time(now(), "-0d@d")
| eval dateLastMonthUnix=relative_time(now(), "-1mon@mon")
| where last_found >= today AND pathPubDate<dateLastMonthUnix

[jacortijo]

I dont think that relative_time command is giving the date I need.

if today is 9/11, you relative_time command gives 9/10 and I want to get 1/10.

eval dateLastMonthUnix=relative_time(now(), "-1mon@mon")