Miscellaneous Linux commands. Some useful tips for the Linux BASH prompt.

The ldd command will print out a list of all libraries that an executable is linked against. This is the output for a simple “Hello World” command.

20:15:31 tux@linux-v415 ($ ldd ./a.out 
        linux-vdso.so.1 =>  (0x00007fff171ff000)
        libc.so.6 => /lib64/libc.so.6 (0x00007fe56ef58000)
        /lib64/ld-linux-x86-64.so.2 (0x00007fe56f2e8000)
20:15:49 tux@linux-v415 ($

If you wish to view a graphical representation of your system load in an Xterm or on the text console, use the tload command. This prints the graph using text characters.

To send a broadcast message from your tty or terminal emulator window use the wall command. I tried this on my KDE desktop in the konsole window and the notification popped up from the system tray showing my message. Just type the intended message and then press Ctrl-D to send it.

10:01:58 tux@linux-v415 ($ wall
Hello
 
Broadcast Message from tux@linux-v4                                            
        (/dev/pts/1) at 10:02 ...                                              
 
Hello                                                                          
 
10:02:10 tux@linux-v415 ($

The lsblk command will list all of the block devices or hard disks that are mounted on your machine. This is a useful command.

ubuntu ~ $ lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda    202:0    0  30G  0 disk
└─xvda1 202:1    0  30G  0 part /

Here is an interesting command that will reverse any text fed into it. The rev command could be useful when piping text into it to reverse a text file.

10:32:21 tux@linux-v415 ($ rev 
Hello
olleH
Hello
olleH

The ddate command will convert Gregorian dates into Discordian date formats. An example is shown below.

11:01:10 tux@linux-v415 ($ ddate 
Today is Boomtime, the 53rd day of Bureaucracy in the YOLD 3178

To see how much free RAM you have on your Linux system use the free command. This is useful to keep track of memory usage. Another way is to use the cat /proc/meminfo | grep MemFree: command.

11:01:18 tux@linux-v415 ($ free 
             total       used       free     shared    buffers     cached
Mem:       6053668    5902464     151204          0     549500    3353780
-/+ buffers/cache:    1999184    4054484
Swap:      2559996       2240    2557756

Do you sometimes want to find where a program is installed to? The whereis command will help you with this.

11:19:15 tux@linux-v415 ($ whereis emacs
emacs: /usr/bin/emacs /usr/lib/emacs /usr/bin/X11/emacs /usr/share/emacs /usr/share/man/man1/emacs.1.gz

I am not sure if I have posted this before; but the host command will print information about a certain network host. It prints all of the IP addresses and other pertinent information about the target host.

11:21:54 tux@linux-v415 ($ host localhost
localhost has address 127.0.0.1
localhost has IPv6 address ::1
11:22:02 tux@linux-v415 ($ host google.com
google.com has address 74.125.237.105
google.com has address 74.125.237.110
google.com has address 74.125.237.96
google.com has address 74.125.237.97
google.com has address 74.125.237.98
google.com has address 74.125.237.99
google.com has address 74.125.237.100
google.com has address 74.125.237.101
google.com has address 74.125.237.102
google.com has address 74.125.237.103
google.com has address 74.125.237.104
google.com has IPv6 address 2404:6800:4006:803::1002
google.com mail is handled by 30 alt2.aspmx.l.google.com.
google.com mail is handled by 40 alt3.aspmx.l.google.com.
google.com mail is handled by 50 alt4.aspmx.l.google.com.
google.com mail is handled by 10 aspmx.l.google.com.
google.com mail is handled by 20 alt1.aspmx.l.google.com.

To get help on the BASH shell builtin commands the help command is your friend. Type help kill to get help on the kill command for example.

ubuntu ~ $ help help
help: help [-dms] [pattern ...]
    Display information about builtin commands.
 
    Displays brief summaries of builtin commands.  If PATTERN is
    specified, gives detailed help on all commands matching PATTERN,
    otherwise the list of help topics is printed.
 
    Options:
      -d        output short description for each topic
      -m        display usage in pseudo-manpage format
      -s        output only a short usage synopsis for each topic matching
        PATTERN
 
    Arguments:
      PATTERN   Pattern specifiying a help topic
 
    Exit Status:
    Returns success unless PATTERN is not found or an invalid option is given.

If you are very new to the Linux command line, the man intro command will print a helpful tutorial that will help you learn the basics.

If you want to have some fun as I did; make a copy of a text file and then use the join command to join them together…

11:30:50 tux@linux-v415 ($ join my.c my2.c 
#include <stdio.h> <stdio.h>
#include <stdio.h> <sys/times.h>
#include <sys/times.h> <stdio.h>
#include <sys/times.h> <sys/times.h>
 
clock_t times(struct tms *buf); times(struct tms *buf);
 
int main(void) main(void)
{
write(1, "Hello World.\n", 15); "Hello World.\n", 15);
 
return 0; 0;
}
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