Commands by olorin (9)

  • Configures screen to always display the clock in the last line (has to be configured only once). After that you not only have got the possibility to detach sessions and run them in background, but also have got a nice clock permanently on your screen.


    4
    echo 'hardstatus alwayslastline " %d-%m-%y %c:%s | %w"' >> $HOME/.screenrc; screen
    olorin · 2011-02-16 08:04:56 0
  • If you provide the option -t to the script command and redirect stderr into a file, the timing information on what is going on on the terminal, is also stored. You can replay the session via the scriptreplay command, where you can also provide a speedup factor (see the man page for details). Great for demonstration purposes ...


    23
    script -t /tmp/mylog.out 2>/tmp/mylog.time; <do your work>; <CTRL-D>; scriptreplay /tmp/mylog.time /tmp/mylog.out
    olorin · 2011-01-19 07:16:30 8
  • As an alternative to using an additional grep -v grep you can use a simple regular expression in the search pattern (first letter is something out of the single letter list ;-)) to drop the grep command itself. Show Sample Output


    69
    ps aux | grep [p]rocess-name
    olorin · 2009-08-13 05:44:45 10
  • Within /proc and /sys there are a lot of subdirectories, which carry pseudofiles with only one value as content. Instead of cat-ing all single files (which takes quite a time) or do a "cat *" (which makes it hard to find the filename/content relation), just grep recursively for . or use "grep . /blabla/*" (star instead of -r flag). For better readability you might also want to pipe the output to "column -t -s : ". Show Sample Output


    4
    grep -r . /sys/class/net/eth0/statistics
    olorin · 2009-08-05 08:20:39 0
  • Get the name of the parent command. This might be helpful, if you need to react on that information. E. g. a script called directly via ssh has got sshd as parent, manually invoked the parent process will probably be bash


    4
    ps -o comm= -p $(ps -o ppid= -p $$)
    olorin · 2009-08-03 07:41:21 2
  • If you are doing some tests which require reboots (e. g. startup skripts, kernel module parameters, ...), this is very time intensive, if you have got a hardware with a long pre-boot phase due to hardware checks. At this time, kexec can help, which only restarts the kernel with all related stuff. First the kernel to be started is loaded, then kexec -e jumps up to start it. Is as hard as a reboot -f, but several times faster (e. g. 1 Minute instead of 12 on some servers here). Show Sample Output


    21
    /sbin/kexec -l /boot/$KERNEL --append="$KERNELPARAMTERS" --initrd=/boot/$INITRD; sync; /sbin/kexec -e
    olorin · 2009-08-03 07:36:49 2
  • Instead of calculating the offset and providing an offset option to mount, let lomount do the job for you by just providing the partition number you would like to loop mount.


    4
    lomount -diskimage /path/to/your/backup.img -partition 1 /mnt/foo
    olorin · 2009-07-22 11:32:52 1
  • You got some results in two variables within your shell script and would like to find the differences? Changes in process lists, reworked file contents, ... . No need to write to temporary files. You can use all the diff parameters you'll need. Maybe anything like $ grep "^>" is helpful afterwards.


    27
    diff <(echo "$a") <(echo "$b")
    olorin · 2009-07-15 07:26:23 2
  • Let dd use direct I/O to write directly to the disk without any caching. You'll encounter very different results with different block sizes (try with 1k, 4k, 1M, ... and appropriate count values).


    0
    time dd if=/dev/zero of=blah.out oflag=direct bs=256M count=1
    olorin · 2009-07-15 07:17:32 0

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Get your external IP address if your machine has a DNS entry
Using DynDNS or a similar service not only allows access to your home machine from outside without needing to know what IP the ISP has assigned to it but it also comes in handy if you want to know your external IP address. The only purpose of the sed command is to remove the leading "host.na.me has address " part from the output. If you don't need to discard it you can simply use $ host $HOSTNAME

Get your outgoing IP address
Get your external ip adress thanks to http://www.icanhazip.com

Search for files older than 30 days in a directory and list only their names not the full path

Ctrl+S Ctrl+Q terminal output lock and unlock
These are simple shortcuts to pause and continue terminal output, works in most terminals and screen multiplexers like screen. You can use it to catch something if things change too fast, and scroll with Shift + PgUp PgDown. On linux console ScrollLock can also be used.

Reverse SSHfs mount,
While `sshfs $REMOTE_HOST:$REMOTE_PATH $LOCAL_PATH` "pulls" a directory from the remote server to the local host, the above command does the reverse and "pushes" a directory from the local host to the remote server. This makes use of the "slave" option of sshfs which instructs it to communicate over plain stdin/stdout and the `dpipe` tool from vde2 to connect the sftp-server stdout to the sshfs stdin and vice-versa.

Reset hosed terminal,
stty sane resets the tty to basic usable function. The ^J is a newline -- sometimes CR/LF interpretation is broken so use the ^J explicitly.

Test file system performance
You need bonnie++ package for this. More detail than a simple hdparm -t /dev/sda would give you. the -d is the directory where it performs writes/reads for example I use /tmp/scratch with 777 permissions Bonnie++ benchmarks three things: data read and write speed, number of seeks that can be performed per second, and number of file metadata operations that can be performed per second.

Sync the date of one server to that of another.
(Useful when firewalls prevent you from using NTP.)


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