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Securing Linux laptops
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APMSLEEP(1) General Commands Manual APMSLEEP(1) NAME
apmsleep - go into suspend or standby mode and wake-up later SYNOPSIS
apmsleep [-sSnwhVd] [--suspend] [--standby] [--noapm] [--wait] [--precise] [--help] [--version] [--debug] [+]hh:mm DESCRIPTION
Some computers, especially laptops, can wake-up from a low-power suspend to DRAM mode using the Real-time-clock (RTC) chip. Apmsleep can be used to set the alarm time in the RTC and to go into suspend or standby mode. An interrupt from the RTC causes the computer to wake-up. The program detects this event, by waiting for a leap in the kernel time and terminates successfully. If no time leap occurs within one minute, or something goes wrong, the exit value will be non-zero. The wake-up time can be specified in two formats: +hh:mm specifies a relative offset to the current time. The computer will suspend for exactly hh hours and mm minutes plus a few seconds to wake up. On some laptops, the timing is not completely accurate so it may be a few minutes (or more?) late. hh:mm specifies absolute local time in 24-hour format. The time stored in the RTC is not important. You may change the time zone used, with the TZ environment variable as usual. Daylight saving time is not obeyed in this version, but might be in a future release. WARNING: Do not close cover of laptop after suspending the laptop with apmsleep. Most laptops overheat when running with closed cover. Energy conservation with APM is little for a desktop. Turning of the screen will save 1/2, going into standby with drives turned off will save another 1/6th of the current. -V, --version Print the apmsleep program version and exit immediately. -s, --suspend Put the machine into suspend mode if possible (default). On my laptop, suspend mode turns off everything except the memory. -S, --standby Put the machine into standby mode if possible. On my laptop, standby mode turns off screen, hard disk, and CPU. -w, --wait Wait indefinitely for the time leap. -p, --precise Wait for alarm time to match actual time. Do not wait for time leap. This might be useful even without APM. -n, --noapm Do not call apm bios to suspend computer, just set the alarm clock and wait for time leap indefinitely. -d, --debug Print some information about what is going on. REQUIRED SYSTEM CONFIGURATION
Kernel The special character device /dev/rtc must exist and the Linux kernel needs to be compiled with APM and RTC support (CONFIG_RTC, and relevant CONFIG_APM* options). BIOS The computer must have the 'suspend to RAM' feature enabled in the BIOS; 'suspend to Disk' will not work, because the computer is turned off completely. You do not need to enable the ALARM timer, it will be activated by apmsleep. On some boards, you can config- ure which interrupts can be used to awake from suspend mode. If you have such a board, you might want to make sure that keyboard (IRQ 1) and RTC (IRQ 8) are among those interrupts. If your computer does not wake up, try to enable 'modem ring' in the BIOS, even if you do not have a modem. Privileges The program must be run as root or have the SUID attribute set (see chmod(1)). BUGS
Apmsleep cannot detect which event terminated the suspension. Possible events are: keyboard or mouse activity, modem ring, alarm from RTC, any other interrupt. Sometimes, the time leap is not detected properly (causing a wrong exit value). Should use APM BIOS calls to set alarm clock (not yet supported by kernel). This program was tested on a Winbook XL laptop (Pentium) only. It may not function on your hardware. AUTHOR
Written by Peter Englmaier (ppe@mpe.mpg.de) and may be freely distributed under the terms of the GNU General Public License. The code is based on Paul Gortmacher's RTC test/example program. There is ABSOLUTELY NO WARRANTY for this program. The current maintainer is Peter Englmaier. SEE ALSO
xapm(1), apmd(8),rtc.txt(Linux Kernel Documentation) APM
sleep in APM suspend/standby mode APMSLEEP(1)
