path: root/Documentation/power/swsusp.txt
diff options
Diffstat (limited to 'Documentation/power/swsusp.txt')
1 files changed, 44 insertions, 7 deletions
diff --git a/Documentation/power/swsusp.txt b/Documentation/power/swsusp.txt
index b28b7f04abb8..d7814a113ee1 100644
--- a/Documentation/power/swsusp.txt
+++ b/Documentation/power/swsusp.txt
@@ -17,6 +17,11 @@ Some warnings, first.
* but it will probably only crash.
* (*) suspend/resume support is needed to make it safe.
+ *
+ * If you have any filesystems on USB devices mounted before suspend,
+ * they won't be accessible after resume and you may lose data, as though
+ * you have unplugged the USB devices with mounted filesystems on them
+ * (see the FAQ below for details).
You need to append resume=/dev/your_swap_partition to kernel command
line. Then you suspend by
@@ -27,19 +32,18 @@ echo shutdown > /sys/power/disk; echo disk > /sys/power/state
echo platform > /sys/power/disk; echo disk > /sys/power/state
+. If you have SATA disks, you'll need recent kernels with SATA suspend
+support. For suspend and resume to work, make sure your disk drivers
+are built into kernel -- not modules. [There's way to make
+suspend/resume with modular disk drivers, see FAQ, but you probably
+should not do that.]
If you want to limit the suspend image size to N bytes, do
echo N > /sys/power/image_size
before suspend (it is limited to 500 MB by default).
-Encrypted suspend image:
-If you want to store your suspend image encrypted with a temporary
-key to prevent data gathering after resume you must compile
-crypto and the aes algorithm into the kernel - modules won't work
-as they cannot be loaded at resume time.
Article about goals and implementation of Software Suspend for Linux
@@ -333,4 +337,37 @@ init=/bin/bash, then swapon and starting suspend sequence manually
usually does the trick. Then it is good idea to try with latest
vanilla kernel.
+Q: How can distributions ship a swsusp-supporting kernel with modular
+disk drivers (especially SATA)?
+A: Well, it can be done, load the drivers, then do echo into
+/sys/power/disk/resume file from initrd. Be sure not to mount
+anything, not even read-only mount, or you are going to lose your
+Q: How do I make suspend more verbose?
+A: If you want to see any non-error kernel messages on the virtual
+terminal the kernel switches to during suspend, you have to set the
+kernel console loglevel to at least 5, for example by doing
+ echo 5 > /proc/sys/kernel/printk
+Q: Is this true that if I have a mounted filesystem on a USB device and
+I suspend to disk, I can lose data unless the filesystem has been mounted
+with "sync"?
+A: That's right. It depends on your hardware, and it could be true even for
+suspend-to-RAM. In fact, even with "-o sync" you can lose data if your
+programs have information in buffers they haven't written out to disk.
+If you're lucky, your hardware will support low-power modes for USB
+controllers while the system is asleep. Lots of hardware doesn't,
+however. Shutting off the power to a USB controller is equivalent to
+unplugging all the attached devices.
+Remember that it's always a bad idea to unplug a disk drive containing a
+mounted filesystem. With USB that's true even when your system is asleep!
+The safest thing is to unmount all USB-based filesystems before suspending
+and remount them after resuming.