Friday, September 8, 2017

How to install tcsh or csh shell on a Debian or Ubuntu Linux ?

Cshell is a shell (command interpreter) with C-like syntax.

csh is a command language interpreter incorporating a history mechanism , job control facilities , interactive file name and user name completion, and a C-like syntax. It is used both as an interactive login shell and a shell script command processor. tcsh is an enhanced but completely compatible version of the Berkeley UNIX C shell.

"tcsh" advantages

   - The ability to use multiline aliases and exec statements in a reliable and consistent way.                          (Hense "sh" scripts can be  re-written as tcsh scripts with aliases instead of functions.)
   - "tcsh" is the same on all machines.  For "csh" I typically  have to modify scripts for different machines.  [example: HP-UX  "set nonomatch" needs to be replaced by "set nonomatch = ()"] 
   - source code is freely available
   - PWD and other common environmental variables are always defined. With "csh" this depends on the machine.

In most cases csh / tcsh is installed by default. All you have to do is type shell name to start using it:

$ csh

OR
$ tcsh

Install csh / tcsh

In case csh is not installed, type the following command at shell prompt as per your Linux distro / version.

Install it on Debian/Ubuntu/Mint Linux

$ sudo apt-get install csh

Install it on CentOS/RHEL

# yum install tcsh

Install it on Fedora Linux

$ sudo dnf install tcsh
Set csh as default login shell
To make csh as default login shell, type the following command:
$ which tcsh
OR
$ which csh
Sample output:
/bin/csh
Note down the /bin/csh or /bin/tcsh path. To change the shell simply type
$ chsh
OR
$ chsh -s /bin/csh


Thursday, September 7, 2017

How do I display the list of loaded Linux Kernel modules or device drivers on Linux ?

You need to use lsmod program which show the status of loaded modules in the Linux Kernel. Linux kernel use a term modules for all hardware device drivers.Please note that lsmod is a trivial program which nicely formats the contents of the /proc/modules, showing what kernel modules are currently loaded.

List or display loaded modules

Method 1: less /proc/modules

EXAMPLE:

ram@linuxforfreshers.com#less /proc/modules
uas 24576 0 - Live 0x0000000000000000
usb_storage 69632 1 uas, Live 0x0000000000000000
bridge 126976 0 - Live 0x0000000000000000
stp 16384 1 bridge, Live 0x0000000000000000
llc 16384 2 bridge,stp, Live 0x0000000000000000
xt_CHECKSUM 16384 3 - Live 0x0000000000000000
ipt_MASQUERADE 16384 9 - Live 0x0000000000000000
nf_nat_masquerade_ipv4 16384 1 ipt_MASQUERADE, Live 0x0000000000000000
ebtable_nat 16384 0 - Live 0x0000000000000000
ebtables 36864 1 ebtable_nat, Live 0x0000000000000000
nf_log_ipv4 16384 0 - Live 0x0000000000000000
nf_log_common 16384 1 nf_log_ipv4, Live 0x0000000000000000
xt_tcpudp 16384 13 - Live 0x0000000000000000
ip6table_mangle 16384 0 - Live 0x0000000000000000
iptable_nat 16384 1 - Live 0x0000000000000000
nf_conntrack_ipv4 16384 3 - Live 0x0000000000000000


Method 2: lsmod

Example:

ram@linuxforfreshers.com# lsmod  | tail -10
hid_generic            16384  0
usbhid                 49152  0
psmouse               126976  0
hid                   118784  2 hid_generic,usbhid
pata_acpi              16384  0
floppy                 73728  0
fjes                   28672  0
e1000e                233472  0
ptp                    20480  1 e1000e
pps_core               20480  1 ptp

Finding more info about any module or driver

Using Modinfo

Syntax: modinfo driver-Name-Here

Example:

ram@linuxforfreshers.com#modinfo e1000e
filename:       /lib/modules/4.4.0-59-generic/kernel/drivers/net/ethernet/intel/e1000e/e1000e.ko
version:        3.2.6-k
license:        GPL
description:    Intel(R) PRO/1000 Network Driver
author:         Intel Corporation, <linux.nics@intel.com>
srcversion:     8D9E9AFD67E40CA48E61582
alias:          pci:v00008086d000015D6sv*sd*bc*sc*i*
alias:          pci:v00008086d000015E3sv*sd*bc*sc*i*
alias:          pci:v00008086d000015D8sv*sd*bc*sc*i*
alias:          pci:v00008086d000015D7sv*sd*bc*sc*i*
alias:          pci:v00008086d000015B9sv*sd*bc*sc*i*
alias:          pci:v00008086d000015B8sv*sd*bc*sc*i*
alias:          pci:v00008086d000015B7sv*sd*bc*sc*i*
alias:          pci:v00008086d00001570sv*sd*bc*sc*i*
alias:          pci:v00008086d0000156Fsv*sd*bc*sc*i*
alias:          pci:v00008086d000015A3sv*sd*bc*sc*i*
alias:          pci:v00008086d000015A2sv*sd*bc*sc*i*
alias:          pci:v00008086d000015A1sv*sd*bc*sc*i*
alias:          pci:v00008086d000015A0sv*sd*bc*sc*i*
alias:          pci:v00008086d00001559sv*sd*bc*sc*i*
alias:          pci:v00008086d0000155Asv*sd*bc*sc*i*
alias:          pci:v00008086d0000153Bsv*sd*bc*sc*i*
alias:          pci:v00008086d0000153Asv*sd*bc*sc*i*
alias:          pci:v00008086d00001503sv*sd*bc*sc*i*
alias:          pci:v00008086d00001502sv*sd*bc*sc*i*
alias:          pci:v00008086d000010F0sv*sd*bc*sc*i*
alias:          pci:v00008086d000010EFsv*sd*bc*sc*i*
alias:          pci:v00008086d000010EBsv*sd*bc*sc*i*
alias:          pci:v00008086d000010EAsv*sd*bc*sc*i*
alias:          pci:v00008086d00001525sv*sd*bc*sc*i*
alias:          pci:v00008086d000010DFsv*sd*bc*sc*i*
alias:          pci:v00008086d000010DEsv*sd*bc*sc*i*
alias:          pci:v00008086d000010CEsv*sd*bc*sc*i*
alias:          pci:v00008086d000010CDsv*sd*bc*sc*i*
alias:          pci:v00008086d000010CCsv*sd*bc*sc*i*
alias:          pci:v00008086d000010CBsv*sd*bc*sc*i*
alias:          pci:v00008086d000010F5sv*sd*bc*sc*i*
alias:          pci:v00008086d000010BFsv*sd*bc*sc*i*
alias:          pci:v00008086d000010E5sv*sd*bc*sc*i*
alias:          pci:v00008086d0000294Csv*sd*bc*sc*i*
alias:          pci:v00008086d000010BDsv*sd*bc*sc*i*
alias:          pci:v00008086d000010C3sv*sd*bc*sc*i*
alias:          pci:v00008086d000010C2sv*sd*bc*sc*i*
alias:          pci:v00008086d000010C0sv*sd*bc*sc*i*
alias:          pci:v00008086d00001501sv*sd*bc*sc*i*
alias:          pci:v00008086d00001049sv*sd*bc*sc*i*
alias:          pci:v00008086d0000104Dsv*sd*bc*sc*i*
alias:          pci:v00008086d0000104Bsv*sd*bc*sc*i*
alias:          pci:v00008086d0000104Asv*sd*bc*sc*i*
alias:          pci:v00008086d000010C4sv*sd*bc*sc*i*
alias:          pci:v00008086d000010C5sv*sd*bc*sc*i*
alias:          pci:v00008086d0000104Csv*sd*bc*sc*i*
alias:          pci:v00008086d000010BBsv*sd*bc*sc*i*
alias:          pci:v00008086d00001098sv*sd*bc*sc*i*
alias:          pci:v00008086d000010BAsv*sd*bc*sc*i*
alias:          pci:v00008086d00001096sv*sd*bc*sc*i*
alias:          pci:v00008086d0000150Csv*sd*bc*sc*i*
alias:          pci:v00008086d000010F6sv*sd*bc*sc*i*
alias:          pci:v00008086d000010D3sv*sd*bc*sc*i*
alias:          pci:v00008086d0000109Asv*sd*bc*sc*i*
alias:          pci:v00008086d0000108Csv*sd*bc*sc*i*
alias:          pci:v00008086d0000108Bsv*sd*bc*sc*i*
alias:          pci:v00008086d0000107Fsv*sd*bc*sc*i*
alias:          pci:v00008086d0000107Esv*sd*bc*sc*i*
alias:          pci:v00008086d0000107Dsv*sd*bc*sc*i*
alias:          pci:v00008086d000010B9sv*sd*bc*sc*i*
alias:          pci:v00008086d000010D5sv*sd*bc*sc*i*
alias:          pci:v00008086d000010DAsv*sd*bc*sc*i*
alias:          pci:v00008086d000010D9sv*sd*bc*sc*i*
alias:          pci:v00008086d00001060sv*sd*bc*sc*i*
alias:          pci:v00008086d000010A5sv*sd*bc*sc*i*
alias:          pci:v00008086d000010BCsv*sd*bc*sc*i*
alias:          pci:v00008086d000010A4sv*sd*bc*sc*i*
alias:          pci:v00008086d0000105Fsv*sd*bc*sc*i*
alias:          pci:v00008086d0000105Esv*sd*bc*sc*i*
depends:        ptp
intree:         Y
vermagic:       4.4.0-59-generic SMP mod_unload modversions
parm:           debug:Debug level (0=none,...,16=all) (int)
parm:           copybreak:Maximum size of packet that is copied to a new buffer on receive (uint)
parm:           TxIntDelay:Transmit Interrupt Delay (array of int)
parm:           TxAbsIntDelay:Transmit Absolute Interrupt Delay (array of int)
parm:           RxIntDelay:Receive Interrupt Delay (array of int)
parm:           RxAbsIntDelay:Receive Absolute Interrupt Delay (array of int)
parm:           InterruptThrottleRate:Interrupt Throttling Rate (array of int)
parm:           IntMode:Interrupt Mode (array of int)
parm:           SmartPowerDownEnable:Enable PHY smart power down (array of int)
parm:           KumeranLockLoss:Enable Kumeran lock loss workaround (array of int)
parm:           WriteProtectNVM:Write-protect NVM [WARNING: disabling this can lead to corrupted NVM] (array of int)
parm:           CrcStripping:Enable CRC Stripping, disable if your BMC needs the CRC (array of int)


Method 3:

Using following command to find list of installed drivers.

ls -l /lib/modules/$(uname -r)/kernel/drivers/

Example:

ram@linuxforfreshers.com#ls  /lib/modules/$(uname -r)/kernel/drivers/ | tail -10
usb
uwb
vfio
vhost
video
virtio
vme
w1
watchdog
xen

What is the standard directory for driver files are stored?

Using following command u can get standard Directory for Driver files are stored.

echo "Kernel drivers dir: \"/lib/modules/$(uname -r)/kernel/drivers/\" \ for Linux kernel version \"$(uname -r)\" "

Example:

ram@linuxforfreshers.com#echo "Kernel drivers dir: \"/lib/modules/$(uname -r)/kernel/drivers/\" \ for Linux kernel version \"$(uname -r)\" "
Kernel drivers dir: "/lib/modules/4.4.0-59-generic/kernel/drivers/" \ for Linux kernel version "4.4.0-59-generic"





Friday, June 30, 2017

how to find physical location of mysql database under linux?

If you are using MySQL, and want to know the actual physical path of MySQL, where MySQL stores the db, and its information files and the amount of data for MySQL data and MySQL index files i.e. table_name.MYD and table_name.MYI respectively, below is the easy solution.

Default MySQL Physical Directory Path is
/var/lib/mysql/ or /var/db/mysql

You can open it in Terminal  (using sudo or root access). Once you get into the folder, you can easily find the folders which are actually your database names, and in the database name folders, you can find the table names, having MYD and MYI extensions, which are actually your data and index files.




You can use the following command to locate MySQL datadir:

Method 1:

deba@linuxforfreshers.com>>grep datadir /etc/mysql/my.cnf

Sample output
datadir                        = /var/lib/mysql

Method 2:


deba@linuxforfreshers.com>>ps -eo cmd,args | grep mysql

Sample output:

/bin/sh /usr/bin/mysqld_saf /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock --log-error=/var/log/mysqld.log --pid-file=/var/run/mysqld/mysqld.pid --user=mysql
/usr/libexec/mysqld --based /usr/libexec/mysqld --basedir=/usr
--datadir=/var/lib/mysql --user=mysql --pid-file=/var/run/mysqld/mysqld.pid --skip-external-locking --socket=/var/lib/mysql/mysql.sock



Method 3:

mysql -u root -p

mysql> select @@datadir;
+-----------------+
| @@datadir       |
+-----------------+
| /var/lib/mysql/ |
+-----------------+
1 row in set (0.00 sec)


This output confirms that MySQL is configured to use the default data directory, /var/lib/mysql/.

Wednesday, June 28, 2017

how to Allow A Normal User To Run Commands As root Under Linux ?

You need to use the sudo command which is use to execute a command as another user. It allows a permitted user to execute a command as the superuser or another user, as specified in the /etc/sudoers (config file that defines or list of who can run what) file. The sudo command allows users to do tasks on a Linux system as another user.

sudo command

sudo is more more secure than su command. By default it logs sudo usage, command and arguments in /var/log/secure (Red Hat/Fedora / CentOS Linux) or /var/log/auth.log (Ubuntu / Debian Linux).
If the invoking user is root or if the target user is the same as the invoking user, no password is required. Otherwise, sudo requires that users authenticate themselves with a password by default. Once a user has been authenticated, a timestamp is updated and the user may then use sudo without a password for a short period of time (15 minutes unless overridden in sudoers).

/etc/sudoers Syntax

Following is general syntax used by /etc/sudoers file:
USER HOSTNAME=COMMAND
Where,
      USER: Name of normal user
      HOSTNAME: Where command is allowed to run. It is the hostname of the system where this rule applies. sudo is designed so you can use one sudoers file on all of your systems. This space allows you to set per-host rules.
      COMMAND: A simple filename allows the user to run the command with any arguments he/she wishes. However, you may also specify command line arguments (including wildcards). Alternately, you can specify “” to indicate that the command may only be run without command line arguments.

How do I use sudo?

If there are multiple matching entries in /etc/sudoers, sudo uses the last one. Therefore, if you can execute any command with a password prompt, and you want to be able to execute a particular command without a password prompt, you need the exception last.
myusername ALL = (ALL) ALL
myusername ALL = (root) NOPASSWD: /path/to/my/program

Give user ravi access to halt/shutdown command and restart Apache web server. First, Login as root user. Use visudo command edit the config file:
# visudo
Append the following lines to file:
ravi localhost=/sbin/halt
ravi dbserver=/etc/init.d/apache restart
Save and close file . Now ravi user can restart Apache web server by typing the following command:
$ sudo /etc/init.d/apache restart
Output:
Password:
Restarting apache web server....
The sudo command has logged the attempt to the log file /var/log/secure or /var/log/auth.log file:
# tail -f /var/log/auth.log
Sample outputs:
May 17 08:37:43 debian sudo:       ravi : TTY=pts/4 ; PWD=/home/ravi ; USER=root ; COMMAND=/etc/init.d/apache restart
If ravi want to shutdown computer he needs to type command:
$ sudo /sbin/halt
Output:
Password:
Before running a command with sudo, users usually supply their password. Once authenticated, and if the /etc/sudoers configuration file permits the user access, then the command is run. sudo logs each command run.

Examples:

a) Allow admin to run various commands:
admin ALL=/sbin/halt, /bin/kill, /etc/init.d/httpd
b) Allow user admin to run /sbin/halt without any password i.e. as root without authenticating himself:
admin ALL= NOPASSWD: /sbin/halt,/etc/init.d/mysqld
c) Allow user admin to run any command from /usr/bin directory on the system dev02:
admin dev02 = /usr/bin/*
Example:2
The following steps will help you achieve the desired output:
Create a new script file (replace dir.sh  with your desired script name):
vim ~/dir.sh
The script will be created in the user’s home directory
Add some commands that only a root or sudo user can execute like creating a folder at the root directory level:
mkdir /ravi
Note: Don’t add sudo to these commands. Save and exit (using :wq!)
Assign execute permissions to it using:
sudo chmod u+x dir.sh
Make changes so that this script doesn’t require a password.
Open the sudoers file:
sudo visudo
Add the following line at the end:
ravi ALL=(root) NOPASSWD: /home/ravi/dir.sh
Replace ravi with whatever your username is. Also make sure this is the last line. Save and exit.
Now when running the command add sudo before it like:
sudo ./dir.sh
This will run the commands inside the script file without asking for a password.