linux – Laurent Schneider

Inline editting

I come from a no-tempfile world, where you getc and putc When moving from legacy Unixes to Linux, inline editting became legend. Number of utilities like sed can now edit the file without tempfile. Your AIX sysadmin probably used to do sed “s/xxx/yyy/” /etc/importantfile > /tmp mv /etc/importantfile /tmp which works… BUT it has a… Continue reading Inline editting

grep color

When you move away from commercial UNIX to Linux, some goodies are just fun, even if they are simple and old. Let’s look at grep. By default, the matched pattern is red. But the color could be changed. Some magic regexp could be used to get more than one color $ tnsping DB01 | … Continue reading grep color

sqlplus: error while loading shared libraries: libsqlplus.so: wrong ELF class: ELFCLASS64

This error usually while you do something wrong. Wait, what’s an error when you do everything right? Okay, here it is: You install the instantclient 32 rpm oracle-instantclient12.1-sqlplus-12.1.0.2.0-1.x86_64 On that server, you switch home using oraenv $ . oraenv ORACLE_SID = [oracle] ? DB01 The Oracle base has been set to /u01/app/oracle You start sqlplus… Continue reading sqlplus: error while loading shared libraries: libsqlplus.so: wrong ELF class: ELFCLASS64

network ip calculation with ifconfig

Most *nix are different. I’ll start with a plain Linux output ifconfig eth0 eth0: flags=4163 mtu 1500 inet 93.184.216.34 netmask 255.255.255.0 broadcast 93.184.216.255 to get the network ip, I just bitwise-and the inet and the netmask. To do it with the shell, I convert the ip to an integer and use the & (AND) operator… Continue reading network ip calculation with ifconfig

on input and output file descriptors

Let’s start with some basics. The basics works as well on Unix, Linux and Windows. Later techniques only work on linux/unix $ ls -l hosts -rw-r–r–. 1 root root 211 Oct 5 2015 hosts $ ls -l xxx ls: cannot access xxx: No such file or directory $ read x foo $ Outpout and error… Continue reading on input and output file descriptors

Unix ODBC Sybase

very similar to Unix ODBC Oracle instead of tnsnames, the connections are defined in $SYBASE/interfaces. the odbc.ini must exists as well in $SYBASE. if you test with unixODBC-devel, keep in mind to use /usr/bin/isql and not $SYBASE_OCS/bin/isql $ODBCSYSINI/odbc.ini [syb] Driver = Sybase16 DSN = syb ServerName=SYB01 $ODBCINI/odbcinst.ini [Sybase16] Description = Adaptive Server Enterprise Driver =… Continue reading Unix ODBC Sybase

Unix ODBC Oracle

To connect via ODBC, check https://laurentschneider.com/wordpress/tag/odbc This article is related to Unix/Linux. Often you have a fat client written in C, while java uses JDBC instead of ODBC. Okay, it’s pretty easy, if you have an oracle client, you probably already have libsqora.so.xx.1 in your LD_LIBRARY_PATH. In this case you can connect using ODBC. What… Continue reading Unix ODBC Oracle

disallow pseudo terminal in ssh

Some Oracle documentation wants you to setup ssh with no password and no passphrase. Configuring ssh This is not really something your security admin will like. First, using DSA, which is deprecated and disabled by default in OpenSSH 7.0, is a pretty dump instruction OpenSSH 7.0 and greater similarly disable the ssh-dss (DSA) public key… Continue reading disallow pseudo terminal in ssh

Untrusted X11 forwarding

I wrote a while ago about my security concerns regarding xhost + xterm -display mypc:0 Way back then, I suggested ssh tunnel. SSH is pretty easy to set up, by enabling the X11Forwarding option. In OpenSSH 3.8 release note, 2004, there was a new default . ssh(1) now uses untrusted cookies for X11-Forwarding In the… Continue reading Untrusted X11 forwarding

run sudo, ssh, password, su in simulated interactive mode

Some commands do not like non-interactive mode $ passwd newpassword > newpassword > EOF Changing password for user lsc. Current password for lsc@example.com: passwd: Authentication token manipulation error $ echo oraclepassword | su – oracle standard in must be a tty $ echo sudopassword | sudo su – oracle [sudo] password for lsc: sudo: sorry,… Continue reading run sudo, ssh, password, su in simulated interactive mode

How to really send a script to the background

Let’s check this small script – foo.sh #!/bin/sh echo foo.1:`date` | tee $HOME/tmp/foo.txt sleep 3 echo foo.2:`date` | tee -a $HOME/tmp/foo.txt $ $HOME/tmp/foo.sh foo.1:Thu Nov 27 17:34:53 CET 2014 foo.2:Thu Nov 27 17:34:56 CET 2014 Very obvious, I write to the console, wait three seconds, then write to the console. Ok, let’s take another script… Continue reading How to *really* send a script to the background

fun with cron

Today I find out that my scheduler was too busy to execute all jobs in my crontab !? * * * * * (while :;do ssh example.com :; done) 59 23 19 06 * touch /tmp/bang my while loop is going to produce so much hangs on the cron deamon that it may not be… Continue reading fun with cron

Testing for (non-)empty string in shell

One way to test for (non-)empty string is to use test and -z (-n) $ x=foo $ test -z “$x” $ echo $? 1 This is mostly seen with an if and [ -z … ] syntax $ y=bar $ if [ -n “$y” ]; then echo non-empty; fi non-empty Instead of a variable, it… Continue reading Testing for (non-)empty string in shell

hot to bypass requiretty in sudo

You can execute it a command without password from the commande line $ sudo -l User lsc may run the following commands on this host: (root) NOPASSWD: /usr/local/bin/helloworld $ sudo /usr/local/bin/helloworld Hello World! Now you try to run it via cron and you get sudo: sorry, you must have a tty to run sudo The… Continue reading hot to bypass requiretty in sudo

use cron to schedule a job only once

I wrote about not using DAY OF MONTH and DAY OF WEEK simultanously in how to cron The correct method is to use 15 14 15 05 * /tmp/run-my-job But… I wrote this five years ago. Hmmm ! Not that correct then since it would run every year 😉 Ok, periodically I check for jobs… Continue reading use cron to schedule a job only once

remove the current directory

Can I remove the current directory? I used to believe you cannot. Solaris: $ uname -s SunOS $ mkdir /tmp/bla $ cd /tmp/bla $ rm -r /tmp/bla rm: Cannot remove any directory in the path of the current working directory /tmp/bla $ AIX: $ uname -s AIX $ mkdir /tmp/bla $ cd /tmp/bla $ rm… Continue reading remove the current directory

How to quit crontab -e without overwritting cron

Imagine my crontab * * * * * /usr/bin/date > /tmp/foo I am writing the date to /tmp/foo every minute $ cat /tmp/foo Thu Jul 5 08:45:01 CEST 2012 Now I want to view my crontab in my EDITOR (vi). $ crontab -e I do not quit yet. In the meantime, my colleague modify the… Continue reading How to quit crontab -e without overwritting cron

Check mount option in linux

I did not find a clean way to check the mount option in Linux. For instance wsize=32768 On AIX, I simply type “mount” and see the mount option… For some reasons, my Linux does not show me the complete mount options ! $ mount precision:/nfsserver on /nfsclient type nfs (rw,bg,addr=127.0.0.2) $ grep nfsclient /proc/mounts precision:/nfsserver… Continue reading Check mount option in linux

Check if it a program is already running in Unix

There is more than one way to do it, the safe is probably to check if /home/lsc/OH_YES_I_AM_RUNNING exists and believe it. This is called the file.PID method and is widely used (Apache used to use it since a long long time). It needs file. It needs cleanup if you reboot your server in the middle… Continue reading Check if it a program is already running in Unix

shell and list of files

How do you loop thru a list of files? For instance you want to archive than delete all pdf documents in the current directory : Bad practice : tar cvf f.tar *.pdf rm *.pdf There are multiple issue with the command above 1) new files could come during the tar, so the rm will delete… Continue reading shell and list of files

Generate network graph from command line

I recently wrote on gnuplot, today I tried another command line utility to generate graphs, graphviz, version 2.24.0 on AIX5L. Pretty straightforward syntax : ( echo “digraph Emp {” sqlplus -s -L scott/tiger

send graph per mail from sqlplus

How to send a graph with a single command from your database to your mail in Unix? I tried this (gnuplot is available for Solaris, AIX and most Unix derivates) : echo ‘ set hea off pages 0 feed off prom set title “salaries of EMP” prom unset key prom unset xtics prom unset xlabel… Continue reading send graph per mail from sqlplus

scp tuning

I twitted yesterday : laurentsch copying 1TB over ssh sucks. How do you fastcopy in Unix without installing Software and without root privilege? I got plenty of expert answers. I have not gone to far in recompile ssh and I did not try plain ftp. Ok, let’s try first to transfer 10 files of 100M… Continue reading scp tuning

What is the current setting of NLS_LANG in sqlplus?

I just learnt a neat trick from Oracle Support. How do you see the current value of NLS_LANG in SQLPLUS ? HOST is not the right answer. E.g.: Unix: SQL> host echo $NLS_LANG AMERICAN_SWITZERLAND Windows: SQL> HOST ECHO %NLS_LANG% %NLS_LANG% The correct setting is revealed by @.[%NLS_LANG%] E.g.: Unix: SQL> @.[$NLS_LANG] SP2-0310: unable to open… Continue reading What is the current setting of NLS_LANG in sqlplus?

Time offset in Unix

What is the time offset of the current date in Unix? perl -e ‘ $t=time; @l=localtime($t); @g=gmtime($t); $d=$l[2]-$g[2]+($l[1]-$g[1])/60; $gd=$g[3]+$g[4]*31+$g[5]*365; $ld=$l[3]+$l[4]*31+$l[5]*365; if($gd$ld){$d-=24} print ($d.”\n”)’ 2 Am I in summer (DST)? perl -e ‘if((localtime)[8]){print”yes”}else{print “no”}’ yes

last access time of a file

I was reading http://blogs.oracle.com/myoraclediary and there was a command about printing the modification details of a file. In Linux / Cygwin “stat” exists as a command $ stat /etc/hosts Access: 2010-08-25 15:20:49.782522200 +0200 Modify: 2010-08-18 14:04:25.868114200 +0200 Change: 2010-08-18 14:04:26.072413100 +0200 Or use the one-liner perl below ### st_atime; /* Time of last access */… Continue reading last access time of a file

to cvs or to subversion

First surprise, after migration, the size of my subversion folder is double the size of my cvs folder. With a bunch of 2Gb disks shared amoung dozens of unix persons, and regular reminders the current usage reached 100%, you will feel the pain of having each developers doublesizing its home directory… The reason is a… Continue reading to cvs or to subversion

extract xml from the command line

I just discovered this morning this cool utility in my /bin directory : xmllint You can use it to extract values from your xml files within your shell scripts $ cat foo.xml John Jack $ echo ‘cat //emplist/emp[@no=”1″]/ename/text()’| xmllint –shell foo.xml | sed -n 3p John I like this !

read without Enter

A small unix tip today. Do you want to continue ? If you are expecting “y” or “n” but do not want to enforce the user to type y[Enter] but simply y, you can use the -n option in bash. Within a ksh script: yorn=$(bash -c ‘read -p “Do you want to continue ? “… Continue reading read without Enter

cd

Do you know cd ? I thought I did until this afternoon … OK, let’s start some basic. I create two directories $ echo $SHELL /bin/ksh $ mkdir /tmp/foo $ mkdir /tmp/bar create a symlink /tmp/bar/baz pointing to /tmp/foo $ ln -s /tmp/foo /tmp/bar/baz create a file foo1 in foo $ touch /tmp/foo/foo1 change to… Continue reading cd