Crontab for Fedora / RedHat / CentOS / Ubuntu

Crontab can run scripts at regular intervals and perform various tasks. Those intervals can be from 1 minute to 1 year, repeatedly.

To list current crontabs:

# crontab -l

You can create a crontab file by entering the following terminal command:

 # crontab -e

A crontab file has six fields for specifying minute, hour, day of month, month, day of week and the command to be run at that interval:

#################################################################
#minute (0-59),                                                 #
#|      hour (0-23),                                            #
#|      |       day of the month (1-31),                        #
#|      |       |       month of the year (1-12),               #
#|      |       |       |       day of the week (0-6 with 0=Sun)#
#|      |       |       |       |       commands                #
#################################################################

Some examples:

* * * * * #Runs every minute
*/5 * * * * #Runs at every 5 minutes
30 * * * * #Runs at 30 minutes past the hour
45 6 * * * #Runs at 6:45 am every day
45 18 * * * #Runs at 6:45 pm every day
00 1 * * 0 #Runs at 1:00 am every Sunday
00 1 * * 7 #Runs at 1:00 am every Sunday
00 1 * * Sun #Runs at 1:00 am every Sunday
30 8 1 * * #Runs at 8:30 am on the first day of every month
00 0-23/2 02 07 * #Runs every other hour on the 2nd of July

You can also use some special strings:

@reboot #Runs at boot
@yearly #Runs once a year [0 0 1 1 *]
@annually #Runs once a year [0 0 1 1 *]
@monthly #Runs once a month [0 0 1 * *]
@weekly #Runs once a week [0 0 * * 0]
@daily #Runs once a day [0 0 * * *]
@midnight #Runs once a day [0 0 * * *]
@hourly #Runs once an hour [0 * * * *]

You can use multiple commands for the same crontab:

@daily &&

Specifying a crontab file to use

# crontab -u

Example:

# crontab -u tux ~/crontab

-would set Tux's crontab file to that of the file named "crontab" residing in Tux's home directory.

To remove a crontab file for current user:

# crontab -r

Command Line Wi-Fi for Fedora

[rajat@localhost ~]$ uname -a
Linux localhost.localdomain 2.6.35.6-45.fc14.i686 #1 SMP Mon Oct 18 23:56:17 UTC 2010 i686 i686 i386 GNU/Linux


[root@localhost rajat]# iwlist eth1 scan
eth1      Scan completed :
          Cell 01 - Address: 00:90:4C:91:00:01
                    ESSID:"DevEnablers"
                    Mode:Managed
                    Frequency:2.437 GHz (Channel 6)
                    Quality:1/5  Signal level:-82 dBm  Noise level:-93 dBm
                    IE: IEEE 802.11i/WPA2 Version 1
                        Group Cipher : CCMP
                        Pairwise Ciphers (1) : CCMP
                        Authentication Suites (1) : PSK
                    Encryption key:on
                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
                              24 Mb/s; 36 Mb/s; 54 Mb/s; 6 Mb/s; 9 Mb/s
                              12 Mb/s; 48 Mb/s
what is available in your area.

#iwconfig eth1 essid network-essid

ESSID your route name
NETWORK-ESSID An SSID is a 32-character alphanumeric key uniquely identifying a wireless LAN.

#iwconfig eth1 freq 2.422G
#iwconfig eth1 channel 6


Frequency:2.437 GHz (Channel 6)

iwlist eth1 frequency
eth1      13 channels in total; available frequencies :
          Channel 01 : 2.412 GHz
          Channel 02 : 2.417 GHz
          Channel 03 : 2.422 GHz
          Channel 04 : 2.427 GHz
          Channel 05 : 2.432 GHz
          Channel 06 : 2.437 GHz
          Channel 07 : 2.442 GHz
          Channel 08 : 2.447 GHz
          Channel 09 : 2.452 GHz
          Channel 10 : 2.457 GHz
          Channel 11 : 2.462 GHz
          Channel 12 : 2.467 GHz
          Channel 13 : 2.472 GHz
          Current Channel:6

[root@localhost rajat]# iwlist eth1 bitrate
eth1      12 available bit-rates :
      1 Mb/s
      2 Mb/s
      5.5 Mb/s
      6 Mb/s
      9 Mb/s
      11 Mb/s
      12 Mb/s
      18 Mb/s
      24 Mb/s
      36 Mb/s
      48 Mb/s
      54 Mb/s
          Current Bit Rate=8 Mb/s

Set the maximum number of retries

#iwlist eth1 retry 8

Set maximum lifetime 300 millisecond

#iwconfig eth1 retry lifetime 300m

Set maximum fragment size

#iwconfig eth1 frag 512

Some cards may not apply these settings changes immediately.

#iwconfig eth1 commit

Command line BitTorrent client Fedora / RedHat /CentOS

BitTorrent is the name of a peer-to-peer (P2P) file distribution protocol, and of a free software implementation of that protocol.



[root@example ~]# python -V
Python 2.7

[root@example ~]# yum install bittorrent -y

[root@example ~]# rpm -qa |grep bittorrent

bittorrent-4.4.0-15.fc14.noarch

[root@example rajat]# bittorrent-curses CD704DCEEA6555A6DA95E8EB233E1956C825B8AE.torrent 

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