linux: logging top processes by cpu or memory

I wanted to log the processes consuming cpu and memory

First thought was to use top in the batch mode (-b).
-c to show the process name.
-n 1 to capture for 1, to run for 1 frame
   
$ top -b -c -n 1 > top_$(date +"%Y-%m-%d_%H%M").log

But I was not getting the complete process/command name.

Later I  used the below technique and it was quite helpful

#!/bin/bash

log_file=top_$(date +"%Y-%m-%d_%H%M").log
echo 'user    %cpu    %mem    pid    elapsed time    command' > $log_file
echo ' =========== CPU ===========' > $log_file
ps -eo user,pcpu,pmem,pid,etime,command | sort -rn -k2 | head -11 > $log_file
echo ' ========== MEMORY ==========' >> $log_file
ps -eo user,pcpu,pmem,pid,etime,command | sort -rn -k3 | head -11 >> $log_file

Observation:

1. 'ps aux' is a wonderful command

2. ps command itself has --sort <fieldname>, but there is no reverse sorting

bash script: arithmetic comparison

Arithmetic in BASH is integer math only. You can't do floating point math in Bash; if you need that capability, see Bash FAQ #22.

Remember few tricks

1. use [[ .. ]] for strings and files

2. use (( .. )) for numbers

To compare arithmetic numbers use bc function

$(echo "1.4 < 2.5" | bc)

> and < is for ASCII comparison and so 100 > 75 is false

-gt, -lt is only integer comparison.

This works for me

    if (( $(echo "$mem_util > 75" | bc) == 1 ))
    then
        ...
    fi

I am wondering why there was no floating point support??

References:

http://mywiki.wooledge.org/ArithmeticExpression

http://mywiki.wooledge.org/BashFAQ/031

linux: complete command

I have my .ssh/config with a lot of connection names. What would be better than to have auto complete with ssh <TAB> <TAB>

Added this line to my bash profile and I was good to go.

complete -W "$(awk '/^\s*Host\s*/ { sub(/^\s*Host /, ""); print; }' ~/.ssh/config)" ssh

man complete

There is a lot that human can do, for everything else there is [shell] script :)

rsync - folder to folder

rsync is wonder utility to sync files.

I had a situation and I was sure the developer must have thought of it. And I was right :) He had solved it with a trailing /

rsync [option] /home/foo/bar dest:/home/foo

will sync bar directory of source into destinations /home/foo.

Note: this requires access to /home/foo

Suppose you have /bar under root / of the destination and you want to sync the same source. Now this will get tricky as it is rare to have open access to /. The solution is

rsync [option] /home/foo/bar/ dest:/bar

The trailing / in the source syncs everything under bar and fits the solution to the problem.

linux: RANDOM is so simple

I was impressed with $RANDOM in linux. Simply use $RANDOM to get a random number.

Shell script thingy

Did you know: Hypen, -, is not allowed in script variable names!

a="A"
b="B"

echo "$a_$b"

will print B??!!

it will treat $a_ as the first variable name.

To fix it

echo "${a}_${b}"

Running redis as background process

I am big fan of redis and there are many reasons for it! The first being its simplicity to set up and go live.

Copy the redis.conf from the source and make necessary changes. There are very less configuration keys and they are supported with clean in-line documentation.

To start:
redis-server <location to the redis.conf>

To Stop:
killall -w redis-server

Note:

You might have observed in the conf file. Let me put it here. To run redis as daemon you should configure these two keys

daemonize yes

pidfile /home/<user>/pids/redis.pid

For everything else redis.io