add "Pause all userspace processes"

4 files changed, 56 insertions, 0 deletions

diff --git a/.gitattributes b/.gitattributes
index 176a458..d76765e 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1 +1,3 @@
 * text=auto
+
+*.sh text eol=lf
diff --git a/_posts/2022-09-07-gdb-sleep-all.md b/_posts/2022-09-07-gdb-sleep-all.md
new file mode 100644
index 0000000..b4915d3
--- /dev/null
+++ b/_posts/2022-09-07-gdb-sleep-all.md
@@ -0,0 +1,35 @@
+---
+title: Pause all userspace processes
+excerpt: >
+  How do you pause all userspace processes for a certain amount of time?
+snippets_root_directory: snippets/gdb_sleep_all
+snippets_language: bash
+snippets:
+  main:
+    - gdb_sleep_all.sh
+  gdb:
+    - sleep.gdb
+---
+If you need to debug some kind of monitoring system (or just have some fun),
+you might want to pause all userspace processes for a certain number of seconds
+(to measure delays, etc.).
+
+You can easily do this using GDB like this:
+
+{% include jekyll-theme/snippets/section.html section_id='main' %}
+
+sleep.gdb is a very simple GDB script; it basically sleeps for a determined
+amount of seconds:
+
+{% include jekyll-theme/snippets/section.html section_id='gdb' %}
+
+You can simply run
+
+    sudo ./gdb_sleep_all.sh
+
+and all of your userspace processes should be frozen for 30 seconds.
+
+On a couple of servers, this worked quite well; not so well on my laptop with
+Xfce installed.
+Obviously, this would require a bit of work to adapt for containers as well.
+Otherwise, pretty neat, huh?
diff --git a/_posts/snippets/gdb_sleep_all/gdb_sleep_all.sh b/_posts/snippets/gdb_sleep_all/gdb_sleep_all.sh
new file mode 100755
index 0000000..e923740
--- /dev/null
+++ b/_posts/snippets/gdb_sleep_all/gdb_sleep_all.sh
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+set -o errexit -o nounset -o pipefail
+
+# Select all process IDs that are _not_ children of PID 2, [kthreadd].
+pids="$( ps -o pid --no-headers --ppid 2 -p 2 --deselect )"
+
+for pid in $pids; do
+	cmdline="$( cat "/proc/$pid/cmdline" | tr '\0' ' ' )" || continue
+	echo ------------------------------------------------------------------
+	echo "PID: $pid"
+	echo "Command line: $cmdline"
+	echo ------------------------------------------------------------------
+	gdb -p "$pid" -x sleep.gdb -batch &
+done
+
+wait
diff --git a/_posts/snippets/gdb_sleep_all/sleep.gdb b/_posts/snippets/gdb_sleep_all/sleep.gdb
new file mode 100644
index 0000000..04f17fc
--- /dev/null
+++ b/_posts/snippets/gdb_sleep_all/sleep.gdb
@@ -0,0 +1,2 @@
+shell sleep 30
+quit