Backups: Beep Beep Beep

This post isn’t technical. It’s mostly steam, technical steam. The message is

meant

mostly for end users. I’m decommissioning a server that is barely used. The only user left on the system, after being warned about the decommissioning informs me that the files are mostly corrupted on the system. The system is almost as old as I am and the files in question were changed roughly half a decade ago. Backups, even if they existed are long gone.

It appears that the former owner of the server converted the system to a virtual hypervisor around that time. Why the files are corrupted are beyond me. If files were across the board corrupted then the system would not be booting or giving other errors. Maybe /home was selectively corrupted? That would be very… odd.

Regardless, it’s important to not rely on saving your files on remote servers. Make certain you keep a backup. Verify your content!

QEMU VNC: Change Your Password And Daemonize Your Monitor

I had a lovely time figuring this out. For obvious reasons you don’t pass the vnc password to the qemu command as it can be seen with a ps. The only other approved

unimplemented option is to have a password file. At least with a password file you can secure it with file

system permissions. My box has no users so to me whatever works works. Anyway…

The problem: daemonize your qemu while still allowing vnc with security! To change the vnc password you have to issue a command ‘change vnc password XXXXX’ to the qemu monitor. The monitor can work with stdio but that defeats the point of daemonize…

My solution: set the monitor to use a tcp port bound to localhost. This way you can continue to control the qemu monitor from the tcp socket. Then use netcat’s nc command to issue it the change vnc password command. I ran in to yet another problem. The nc command didn’t automatically exit and my scripts are non interactive start up scripts.

qemu-kvm -vnc 192.168.0.1:0,password -monitor telnet:127.0.0.1:4444,server,nowait –daemonize
echo change vnc password XXXXX; echo | nc 127.0.0.1 4444

Solution to new problem: Tell nc to execute a command rather than use stdio. The command would simply echo command then echo a new line and exit. This also solved my problem of how to tell qemu to stop running without simply issuing it a kill command. My script took arg1 as the vnc password.

nc 127.0.0.1 4444 -e /change_vnc.sh XXXXX

The fact that I’m using busybox to do all of this may have complicated the nc command

so I don’t know if actual netcat

would have had that problem. Regardless it was very simple.

For This: An Ad Hoc Guide To Advanced Latin Networking

This post won’t be Greek to you if you found it by googling your error. Our office network has been very unreliable as of late. Working in a terminal is hell when your latency is 15 seconds. I decided to setup my phone to work as a wifi router. After compiling the rtl8187 module in my 2.6.34 kernel I tried the following command with the resulting error.

root@miar:~# iwconfig wlan1 essid AndroidTether mode ad-hoc
Error for wireless request “Set Mode” (8B06) :
SET failed on device wlan1 ; Operation not supported.

After a bit of looking around I found that the in-kernel rtl8187 module is compiled against the mac80211 library. The new library is apparently more generic and implementation is a bit different. The bottom line is there is no Ad Hoc support for the rtl8187 module. Other modules get around this by implementing adhoc-demo. The adhoc-demo has some limitations too. For example it doesn’t send out beacons. Because of that you have to configure the channel and other settings that would normally be detected in those beacons. To me this is way better than not working at all.

The real root of the problem was that they deprecated the IEEE80211 library that the older drivers used. The newer driver based on the aforementioned mac80211 library may have some limitations too but I’m really only

discussing rtl8187. The older drivers based off the IEEE80211 also require WIRELESS_EXT which is also deprecated. I tried enabling the deprecated kernel modules with success however the older kernel module source would still not compile against the newer kernel. I believe there are other elements that were changed or removed in the more modern 2.6.34 kernel. My recommendation for anyone experiencing these problems may want to voice their concerns in existing bug tickets or if none exist open a bug to get Ad Hoc support officially added in to the module.

On the same page that discussed adhoc-demo

a patch was produced to specifically implement Ad Hoc support to the rtl8187 in-kernel module. There was another interesting patch to add mesh support but I wasn’t really interested in that functionality at the time. Below is the patch I applied that worked to get Ad Hoc support for my (Trend Micro) rtl8187B usb network adapter. Please bare in mind that this patch was taken from a newsgroup posting I found and is a band aid patch to the real problem.

— linux-2.6.x/drivers/net/wireless/rtl818x/rtl8187_dev.c.orig 2010-07-29 14:40:09.000000000 +0300
+++ linux-2.6.x/drivers/net/wireless/rtl818x/rtl8187_dev.c 2010-07-29 14:59:39.000000000 +0300
@@ -1032,6 +1032,7 @@ static int rtl8187_add_interface(struct

switch (vif->type) {
case NL80211_IFTYPE_STATION:
+ case NL80211_IFTYPE_ADHOC:
break;
default:
goto exit;
@@ -1178,7 +1179,10 @@ static void rtl8187_bss_info_changed(str
reg

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= 0;

if (is_valid_ether_addr(info->bssid)) {
– reg |= RTL818X_MSR_INFRA;
+ if (vif->type == NL80211_IFTYPE_ADHOC)
+ reg |= RTL818X_MSR_ADHOC;
+ else
+ reg |= RTL818X_MSR_INFRA;
rtl818x_iowrite8(priv, &priv->map->MSR, reg);
} else {
reg |= RTL818X_MSR_NO_LINK;
@@ -1502,7 +1506,8 @@ static int __devinit rtl8187_probe(struc
* XXX: Once this driver supports anything that requires
* beacons it must implement IEEE80211_TX_CTL_ASSIGN_SEQ.
*/
– dev->wiphy->interface_modes = BIT(NL80211_IFTYPE_STATION);
+ dev->wiphy->interface_modes = BIT(NL80211_IFTYPE_STATION) |
+ BIT(NL80211_IFTYPE_ADHOC);

if ((id->driver_info == DEVICE_RTL8187) && priv->is_rtl8187b)
printk(KERN_INFO “rtl8187: inconsistency between id with OEM”

Once patched my commands executed properly. Remember if you insmoded the rtl8187 module before recompiling with the patch it will remain resident in memory until you rmmod it and insmod it again. I hope you

find this information as useful as I did. Thank you to the original author of the patch!