Crontab format

format of /etc/crontab:

# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed

Disabling weak ciphers in Tomcat

In order to disable weak ciphers, please modify your SSL Connector, container attribute inside server.xml with the following information:


ciphers="SSL_RSA_WITH_RC4_128_SHA,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_DHE_RSA_WITH_AES_128_CBC_SHA,TLS_DHE_DSS_WITH_AES_128_CBC_SHA,SSL_RSA_WITH_3DES_EDE_CBC_SHA,SSL_DHE_RSA_WITH_3DES_EDE_CBC_SHA,SSL_DHE_DSS_WITH_3DES_EDE_CBC_SHA"

How to create zip on ubuntu?

To zip a directory try:

zip -r zipfile.zip directory

How to get Unix Timestamp in Bash?

Simply use: 

date +%s

sed command to Insert a line before the last line of the file.

sudo sed -ie '$ i tomcat7 hard nofile 32768' /etc/security/limits.conf

This command will insert the entry "tomcat7 hard nofile 32768" before the last line of the file limits.conf. 

tar command to preserve file permissions?

Creating Tar: 

tar -pcvzf xxx.tar.gz ABC

Extracting: 

tar -pxvzf xxx.tar.gz ABC


Where, 
p == preserve permissions
c == create archive
v == verbose (print names while making tar)
z == gzip
f == tar file name

How do I log out another logged in user in ubuntu?

Use command: 

sudo pkill -KILL -u username