Commands tagged ruby, bash (1)

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move a lot of files over ssh
copy files to a ssh server with gzip compression

Stoppable sleep
A nice way to interrupt a sleep with a signal.

Getting started with tcpdump
At some point you want to know what packets are flowing on your network. Use tcpdump for this. The man page is obtuse, to say the least, so here are some simple commands to get you started. -n means show IP numbers and don't try to translate them to names. -l means write a line as soon as it is ready. -i eth0 means trace the packets flowing through the first ethernet interface. src or dst w.x.y.z traces only packets going to or from IP address w.x.y.z. port 80 traces only packets for HTTP. proto udp traces only packets for UDP protocol. Once you are happy with each option combine them with 'and' 'or' 'not' to get the effects you want.

Share a terminal screen with others
If you enable multiuser, then you can permit others to share your screen session. The following conditions apply: 1. screen must be suid root; 2. "multiuser on" must be configured in ~/.screenrc; 3. control the others user(s) access with "aclchg": # ----- from ~/.screenrc-users ----- aclchg someuser +rx "#?" #enable r/o access to "someuser" aclchg someuser -x "#,at,aclchg,acladd,acldel,quit" # don't allow these aclchg otheruser +rwx "#?" # enable r/w access to "otheruser" aclchg otheruser -x "#,at,aclchg,acladd,acldel,quit" # don't allow them to use these commands # ----- After doing this (once), you start your session with: $ screen Then, the other user can join your terminal session(s) with youruserid: $ screen -r youruserid/ Note: the trailing "/" is required. Multiple users can share the same screen simultaneously, each with independent access controlled precisely with "aclchg" in the ~/.screenrc file. I use the following setup: # ~/.screenrc-base # default screenrc on any host source $HOME/.screenrc-base source $HOME/.screenrc-$HOST source $HOME/.screenrc-users # ----- Then, the base configurations are in ~/.screenrc-base; the host-specific configurations are in ~/.screenrc-$HOST, and the user configurations are in ~/.screenrc-users. The host-specific .screenrc file might contain some host-specific screen commands; e.g.: # ~/.screen-myhost # ----- screen -t 'anywhere' /bin/tcsh screen -t 'anywhere1' /bin/tcsh # ---- The .screenrc-base contains: # ~/.screenrc-base ## I find typing ^a (Control-a) awkward. So I set the escape key to CTRL-j instead of a. escape ^Jj termcapinfo xterm* ti@:te@: autodetach on zombie kr verbose on multiuser on

find and delete empty dirs, start in current working dir

find the delete file ,which is in use

Nicely display mem usage with ps
Nicely display mem usage with ps.

Sysadmin day date of any given year
Calculate the date of Sysadmin day (last Friday of July) of any given year

Find the package that installed a command

formatting number with comma
it is not work with Cygwin's bash3.X. Test in Linux. use printf "%'f" number while it is floating point number


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