diff --git a/Query-Examples.md b/Query-Examples.md
new file mode 100644
index 0000000..6adf467
--- /dev/null
+++ b/Query-Examples.md
@@ -0,0 +1,89 @@
+
+Query Examples
+==============
+
+As per [Always-on Profiling for Production Systems](https://0x.tools/), the primary tools for querying the CSV files are:
+
+- grep
+- awk
+- cut
+- sort
+- uniq
+
+While grep is primarily used for filtering, this can be done with awk as well.
+
+Both awk and cut can be used to project columns.
+
+The uniq utility is useful for group by, but also for sorting when counts are involved.
+
+
+This command gets the count of occurrences of oraagent.bin, showing which is the most active.
+
+```text
+# awk -F, '/oraagent.bin/ { print $2 }' /var/log/xcapture/2020-12-03.15.csv | sort -n | uniq -c | sort -n
+1 26652
+80 3131
+101 1543
+123 13048
+```
+
+This same thing may also be done in awk:
+
+```text
+# awk -F, '/oraagent.bin/ { freq[$2]++ }END{for (key in freq){print freq[key] ": " key}}' /var/log/xcapture/2020-12-03.15.csv | sort -n
+1: 26652
+80: 3131
+101: 1543
+122: 13048
+```
+
+Here we can see the uniq list of call stacks for PID, along with the count for that stack:
+
+```text
+# awk -F, '/oraagent.bin/ && $2==13048 && $7=="[running]"  && $11 != "" { print $11 }' /var/log/xcapture/2020-12-03.15.csv | sort | uniq -c | sort -n
+  1 ->retint_user()->prepare_exit_to_usermode()->exit_to_usermode_loop()
+  3 ->SyS_nanosleep()->hrtimer_nanosleep()
+  3 ->SyS_poll()->do_sys_poll()->poll_schedule_timeout()
+  6 ->page_fault()->do_page_fault()->__do_page_fault()->call_rwsem_down_read_failed()
+  8 ->SyS_read()->vfs_read()->__vfs_read()->pipe_read()->pipe_wait()
+ 90 ->SyS_futex()->do_futex()->futex_wait()->futex_wait_queue_me()
+```
+
+Breakdown for this command line
+
+`awk -F, '/oraagent.bin/ && $2==13048 && $7=="[running]"  && $11 != "" { print $11 }' /var/log/xcapture/2020-12-03.15.csv | sort | uniq -c | sort -n`
+
+get specify the field separator as a comma
+  `awk -F, `
+
+get only lines that contain oraagent.bin
+  `'/oraagent.bin/ `
+
+continue if the PID = 13048
+  `&& $2==13048 `
+
+continue if the SYSCALL = '[running]'
+  `&& $7=="[running]"`
+
+continue if KSTACK is not empty
+  `&& $11 != "" `
+
+print the KSTACK
+  `{ print $11 }' `
+
+this is the input file
+  `/var/log/xcapture/2020-12-03.15.csv `
+
+sort the output
+  `| sort`
+
+get a count per unique output
+  `| uniq -c `
+
+sort by the count of items
+  `| sort -n`
+
+
+Should you want to do more complex transformations to the data, you may want to use Perl or similar.
+
+
diff --git a/bin/psn b/bin/psn
index 1aaee50..8bfdbe2 100755
--- a/bin/psn
+++ b/bin/psn
@@ -1,5 +1,8 @@
-#!/usr/bin/env python
-#
+#!/usr/bin/env python2
+
+# use the following line on RHEL5 (if you have the additional python26 package installed from EPEL):
+##!/usr/bin/env python26 
+
 #  psn -- Linux Process Snapper by Tanel Poder [https://0x.tools]
 #  Copyright 2019-2021 Tanel Poder
 #  
diff --git a/bin/run_xcapture.sh b/bin/run_xcapture.sh
index 7506312..3f23df5 100755
--- a/bin/run_xcapture.sh
+++ b/bin/run_xcapture.sh
@@ -22,6 +22,11 @@ if [ $# -ne 1 ]; then
   exit 1
 fi
 
+if [ ! -d "$1" ]; then
+	echo "Directory '$1' does not exist"
+	exit 2
+fi
+
 SUDO=sudo # change to empty string if running without sudo
 NICE=-5 # set to 0 if don't want to increase priority
 SLEEP=60
diff --git a/bin/run_xcpu.sh b/bin/run_xcpu.sh
index 48874db..2c04c91 100755
--- a/bin/run_xcpu.sh
+++ b/bin/run_xcpu.sh
@@ -21,13 +21,26 @@ FREQUENCY=1 # 1 Hz sampling
 SUDO=sudo # change to empty string if running without sudo
 NICE=-5
 SLEEP=60
-PERF=/usr/bin/perf
+PERF=$(which perf)
+
+[ -x "$PERF" ] || {
+	echo
+	echo "perf is not installed"
+	echo
+	exit 1
+}
+
 
 if [ $# -ne 1 ]; then
   echo "Usage: $0 output_dir"
   exit 1
 fi
 
+if [ ! -d "$1" ]; then
+	echo "Directory '$1' does not exist"
+	exit 2
+fi
+
 logger "$0 Starting up outdir=$1 nice=$NICE"
 
 while true ; do
diff --git a/bin/schedlat b/bin/schedlat
index 9f4f1aa..879e504 100755
--- a/bin/schedlat
+++ b/bin/schedlat
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 
 # Copyright 2020 Tanel Poder
 # Licensed under the Apache License, Version 2.0 (the "License")