PS: I was using Fluxbox back than! Wow, crazy youth! :)
]]>:( 2 oscar:~#
Cute, a? It even prints the exit code. Useful and cute at the same time! And here is definition of the prompt. As you can see it uses simple function to determine return code of executed command and adjust its feelings accordingly.smiley() {
RC=$?
[[ ${RC} == 0 ]] && echo ':)' || echo ":( ${RC}"
}
export PS1="\$(smiley) \u@\h:\w\\$ "
export PS1="\[\033[0;36m\]\033(0l\033(B\[\033[0m\][\[\033[1;31m\]\u\[\033[0m\]]\[\033[0;36m\]\033(0q\033(B\[\033[0m\][\[\033[1;33m\]@\h\[\033[0m\]]\[\033[0;36m\]\033(0q\033(B\[\033[0m\][\[\033[0;37m\]\T\[\033[0m\]]\[\033[0;36m\]\033(0q\033(B\033(0q\033(B\033(0q\033(B\033(0q\033(B\033(0q\033(B\033(0q\033(B\033(0q\033(B\033(0q\033(B\[\033[0m\][\[\033[1;33m\]\w\[\033[0m\]]\n\[\033[0;36m\]\033(0m\033(B\[\033[0m\]\$ "
Magic! :)
PS: I was using Fluxbox back than! Wow, crazy youth! :)
]]>[root@server ~]# mount -o nouuid /dev/sys/bkp-snap /mnt/misc/
[root@server ~]# dmesg | tail -3
XFS mounting filesystem dm-9
Starting XFS recovery on filesystem: dm-9 (logdev: internal)
Ending XFS recovery on filesystem: dm-9 (logdev: internal)
[root@server ~]# xfs_admin -U generate /dev/sys/bkp-snap
Clearing log and setting UUID
writing all SBs
new UUID = 1bdcf6e1-62fb-47f2-83e4-dc398bb7a1cd
[root@server ~]# dmesg | tail -2
XFS mounting filesystem dm-9
Ending clean XFS mount for filesystem: dm-9
File /proc/meminfo contains a very useful field named Committed_AS. This field indicates TOTAL value of committed memory. If all applications would require all memory allocated to them your server would need this amount of memory.
If we look in the example from my previous post we would find following values:
loreto:/tmp # cat /proc/meminfo
MemTotal: 33274944 kB
…
Committed_AS: 49751960 kB
…
So my server has 32GB of RAM, but total amount of memory allocated is 48GB. That is 150%! If all this memory would be required at once server would crash pretty bad (or OOM killer would start butchering my Oracle databases to get some memory back!). :-)
]]>I quickly logged in to server and checked memory usage:
loreto:/tmp # free
total used free shared buffers cached
Mem: 33274944 32931032 343912 0 20 27013200
-/+ buffers/cache: 5917812 27357132
Swap: 16779884 5603256 11176628
Really only 5GB, check_memory plugin was not wrong. Next this I checked were shared memory segments – Oracle uses shared memory in huge quantities, so this is also very important parameter.
loreto:/tmp # a=0; for i in $(ipcs -m|grep ^0x|awk ‘{print $5}’); do let a+=$i; done; echo $a
20443037885
Ugh, 20GB allocated for shared memory, while system reports only 5GB. Something is very wrong here. Confused, I took out the artillery.
loreto:/tmp # cat /proc/meminfo
MemTotal: 33274944 kB
MemFree: 198580 kB
Buffers: 20 kB
Cached: 27439580 kB
SwapCached: 223880 kB
Active: 16333936 kB
Inactive: 15428724 kB
HighTotal: 32634140 kB
HighFree: 33516 kB
LowTotal: 640804 kB
LowFree: 165064 kB
SwapTotal: 16779884 kB
SwapFree: 10856700 kB
Dirty: 1668 kB
Writeback: 0 kB
AnonPages: 4089416 kB
Mapped: 10222968 kB
Slab: 427584 kB
CommitLimit: 33417356 kB
Committed_AS: 49751960 kB
PageTables: 826016 kB
VmallocTotal: 112632 kB
VmallocUsed: 22228 kB
VmallocChunk: 90180 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
Hugepagesize: 2048 kB
Usually, used memory on Linux is calculated as (Total Memory – (Unused Memory + Buffers + Page Cache)). Why buffers and caches are not counted into memory usage? Simply because it contains data that is not really critical for operating system and applications running. It contains data that can be flushed and removed from the memory at any time.
So in my case that was:
33274944 – (198580 + 20 + 27439580) = 5636764
OK, this matches output from free command. But what about those 20GB of allocated shared memory?
Next few hours I spent in searching and reading Linux documentation on memory management and found few interesting things.
Linux uses principle of memory overcommitment. Basically, what this means is that when application requests memory to be allocated, kernel will always “give: the memory hoping that application will not really use it, or at least not the whole size allocated. Only when application tries to write the data into the memory, kernel will mark the memory as used. This can lead to situation where the size of allocated memory is actually higher than the size of physical memory inside the machine. But as long as there is no demand for allocated memory, system is running without problems.
And this is the core of my dilemma. Shared memory is allocated, but since there is no data in it, it is not counted into used memory.
Memory overcommit can be configured via two parameters:
loreto:/tmp # sysctl -a|grep overcommit
vm.overcommit_ratio = 50
vm.overcommit_memory = 0
From Red Hat manual:
Main news is that now it is possible to change Pidgin status message periodically. Script will go to background (it is a real daemon now :P), change the status, and wait for the set time interval until it changes the message again, and then all over again, wait-change-wait-change.
To change status message every 5 minutes with a random line from file /home/miljan/quotes/dusko_radovic.txt:
pidgin_status.py -d -t 5 -f /home/miljan/quote/dusko_radovic.txt
And in Pidgin you would get something like this every five minutes:
To show the song you are listening to as status message:
pidgin_status.py -s “Mukeka di Rato – Kustapassaaessedrmobral”
And in Pidgin it would look like:
You can see all possible options by running script with -h argument for help.
bleketux, I hope you are still around to enjoy this. ;)
Download: pidgin_status_v2.py
]]>We all know about Nigerian SPAM, but how about American SPAM? :o)
]]>Recently I experienced a very strange problem with one of the RHEL 3 servers we’ve got. Problem manifested in a very strange way, SSH and su logins hanged, other daemons were also hanging during the startup, only way to reboot or shutdown the server was to physically press the restart/power off button, etc. All this could have been caused by problems on both software and hardware level. First suspicious was bad RAID controller, but after tests this proved to be a mislead. After more tests and brainstorms hardware problems were definitely excluded, so problem has to be on the software side. But what could be the problem?
After few more misleading steps I tried to trace system calls created by su command and found very interesting results.
$ strace -f -s 1024 -o /tmp/su.strace.out su -
[-- cut --]
3138 open(”/dev/audit”, O_RDWR) = 3
3138 fcntl64(3, F_GETFD) = 0
3138 fcntl64(3, F_SETFD, FD_CLOEXEC) = 0
3138 ioctl(3, 0×801c406f
And this is where the strace output ends and su command hangs. Audit device file is opened (file descriptor 3) and as soon as the first request is dispatched to this device (ioctl system call to file descriptor 3) command freezes. According to this I should just disable audit on the server and the problem will be gone.
As a test, audit daemon was temporarily stopped and I tried to switch to another user and the problem was indeed gone.
After searching for similar problems with audit daemon I found an article in Red Hat knowledge base regarding the exactly same
issue (http://kbase.redhat.com/faq/FAQ_79_6169.shtm).
From the article:
When the free space in the filesystem holding the audit logs is less than 20%, the above notify command will error out and auditd will enter suspend mode. This causes all system calls to block.
So this behavior is not a bug but actual feature of the software. :o) From security point of view this is expected behaviour – attacker could fill up filesystem where audit logs are stored before the attack and audit will be disabled, meaning no logs of his activity, so better not to allow ANY activity on the system if audit is not able to write to its logs. But still, this kind of behaviour renders the system completely useless to legitimate users.
The topic of this post is not audit, so I will stop here. Important thing is that strace led us directly to the main source of the problem. Resolution of issues like this would be much more complex and time consuming without this great little tool. :)
]]>To cut the long story short, I needed something that will update my Pidgin status message with the information about the current song I am listening. Till recently I was using Rhythmbox player and there is a perfect little Pidgin plugin called Current Track that worked with this player. Last week I discovered gmusicbrowser and fell in love immediately. It is fast, rich with functionalities but still simple to use. Exactly what I want from audio player. (Hm, I just noticed it is written in PERL. Now when Python is used for everything this comes as a big surprise.)
gmusicbrowser already has a plugin called NowPlaying. It will trigger some command whenever song is changed. I just needed to write this command that will inform Pidgin about the change. So, this seemed like a perfect exercise for slow Saturday. :)
Quick search on Pidgin and D-BUS showed extensive documentation about Pidgin API accessible through D-BUS. There is even a working example of how to change the status message! :)
But that was too simple, so I got another idea. Some time ago, I wrote a small daemon in C that will bind to a specific port and display random bofh-excuses fortune messages when someone would telnet to it. (Seems like I have a lot of spare time. I should really find some hobby!) Something similar to telnet bofh.jeffballard.us 666 (here for more information). So I was thinking about implementing the same for my Pidgin status. Random BOFH excuses in your status message! How cool geeky is that!
The result of all that is short (~60 lines of code) Python script that will set your Pidgin status message to:
a) you current song
pidgin_status.py -m The Real McKenzies – Outta Scotch
b) random line from a file
pidgin_status.py -f /usr/local/share/bofh-example
c) anything you give as the command line argument
pidgin_status.py Some very interesting and funny status message
Only difference between a) and c) is the type of the icon that will be shown. In example a) there will be a small musical note, while in example b) and c) nice arrow pointing to right side will be show.
In the middle of testing I noticed this strange message:
Being from Serbia myself, I find this extremely funny. Although, I didn’t know Serbian hackers are so notorious! :)
I hope someone will find it useful. In any case, I am accepting donations for some long and adventurous vacation. As you can see, I really need it! :D
]]>