Effective Linux Commands that Known Lesser

Linux commands are the essence of the entire GNU/Linux operating system used to administer the whole system. You may not know it, but most of the applications you run within the graphical user interface are executing Linux commands for you in the background to accomplish the given task.

strace Command

The strace is a debugging tool which is practised primarily for troubleshooting purpose in Linux. It might not be installed by default in your system, and you may require to apt or yum the essential package.

Trace a command execution using strace command:

root@...... [~]# strace pwd

Sample Output

execve("/bin/pwd", ["pwd"], [/* 29 vars */]) = 0 brk(0) = 0x728000 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0df2000 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=38427, ...}) = 0 mmap(NULL, 38427, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f29b0de8000 close(3) = 0 open("/lib64/libc.so.6", O_RDONLY) = 3 read(3, "7ELF

execve("/bin/pwd", ["pwd"], [/* 29 vars */]) = 0
brk(0) = 0x728000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0df2000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=38427, ...}) = 0
mmap(NULL, 38427, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f29b0de8000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\360\355\1I;\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1922152, ...}) = 0
mmap(0x3b49000000, 3745960, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3b49000000
mprotect(0x3b4918a000, 2093056, PROT_NONE) = 0
mmap(0x3b49389000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x189000) = 0x3b49389000
mmap(0x3b4938e000, 18600, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3b4938e000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de7000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de6000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de5000
....

>
execve("/bin/pwd", ["pwd"], [/* 29 vars */]) = 0
brk(0) = 0x728000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0df2000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=38427, ...}) = 0
mmap(NULL, 38427, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f29b0de8000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\360\355\1I;\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1922152, ...}) = 0
mmap(0x3b49000000, 3745960, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3b49000000
mprotect(0x3b4918a000, 2093056, PROT_NONE) = 0
mmap(0x3b49389000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x189000) = 0x3b49389000
mmap(0x3b4938e000, 18600, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3b4938e000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de7000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de6000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de5000
....

05I;
execve("/bin/pwd", ["pwd"], [/* 29 vars */]) = 0
brk(0) = 0x728000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0df2000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=38427, ...}) = 0
mmap(NULL, 38427, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f29b0de8000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\360\355\1I;\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1922152, ...}) = 0
mmap(0x3b49000000, 3745960, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3b49000000
mprotect(0x3b4918a000, 2093056, PROT_NONE) = 0
mmap(0x3b49389000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x189000) = 0x3b49389000
mmap(0x3b4938e000, 18600, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3b4938e000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de7000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de6000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de5000
....

"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1922152, ...}) = 0
mmap(0x3b49000000, 3745960, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3b49000000
mprotect(0x3b4918a000, 2093056, PROT_NONE) = 0
mmap(0x3b49389000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x189000) = 0x3b49389000
mmap(0x3b4938e000, 18600, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3b4938e000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de7000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de6000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f29b0de5000

The strace command receives a lot of arguments and has many possibilities. Refer to the man page for complete information.

disown -a && exit Command

The system administrators apply a screen command to control jobs working in the terminal background. If you having a long-running job and require to detach from the terminal, you use the screen command to do it. But what if you don’t know how to use the screen, here comes disown command to rescue.
The disown command is used to run the jobs continuously in the background even after you close the terminal session. The syntax of the disown command is:
....

root@...... [~]# Command; disown -a && exit

To detach again the long-running job in the terminal, use the jobs command to find the job number and then use disown %n where n is the job number. To check actually the job is running use ps or top command. The nohup command is an alternative to the disown command.

getconf LONG_BIT Command

The above command presents your machine architecture if it is 32 bit or 64 bit?

root@..... [~]# getconf LONG_BIT

32

Display Date on the Terminal

The below command is a blend of several commands, better say as script. For a person working at a shell or terminal, without GUI seeing the current system date is a tedious job. You have to type the ‘date‘ command to examine today’s date.
Just accomplish the below command on your prompt and see the date and time on the above right corner of the terminal.

root@.... [~]# while sleep 1;do tput sc;tput cup 0 $(($(tput cols)-29));date;tput rc;done &

convert Command

While writing a tutorial, You usually need to produce output, many times in image format. The above command combination does this. If you need the output of tree command (for /etc/x11 directory) in image format. What you want to do terminal is:

root@.....:/etc/X11# tree | convert label:@- /home/avi/tree.png

The output of the above command can be viewed at the specified location (here, the home directory of mine) with the file name specified as tree.png.

watch -t -n1 “date +%T|figlet”

his figlet command was very cool, we will be pipelining ‘figlet‘ to show an animated digital clock in the terminal.
Just check-out yourself, remember you must have figlet installed on the system, do apt or yum to install the required package.

root@..... [~]# watch -t -n1 "date +%T|figlet"

Sample Output

_ ___ ____ ___ _____ _ _ Fri Nov 29 10:29:34 GMT
/ |/ _ \ _|___ \ / _ \ _|___ /| || |
| | | | (_) __) | (_) (_) |_ \| || |_
| | |_| |_ / __/ \__, |_ ___) |__ _|
|_|\___/(_)_____| /_/(_)____/ |_|

host and dig Commands

Although “host” and “dig” command is not that much lesser-known, still not very commonly used. The host command is the DNS lookup utility.

root@.... [~]# host www.google.com

www.google.com has address 173.194.66.147 www.google.com has address 173.194.66.105 www.google.com has address 173.194.66.99 www.google.com has address 173.194.66.104 www.google.com has address 173.194.66.106 www.google.com has address 173.194.66.103 www.google.com has IPv6 address 2a00:1450:400c:c03::68

root@..... [~]# dig www.google.com

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> www.google.com ;; global options: +cmd ;; Got answer: ;; ->>HEADER<

dstat Command

The dstat is a multifaceted tool, that produces statistics relating to system resources. By default, your system might not have ‘dstat‘ installed. Do a apt or yum to install ‘dstat‘ before using this very colorful and description system resource generator.

root@.... [~]# dstat

bind -p Command

The ‘bind -p‘ command will show all the shortcuts available for BASH shell.

root@...... [~]# bind -p

Sample Output

"\C-g": abort "\C-x\C-g": abort "\e\C-g": abort "\C-j": accept-line "\C-m": accept-line # alias-expand-line (not bound) # arrow-key-prefix (not bound) # backward-byte (not bound) "\C-b": backward-char "\eOD": backward-char "\e[D": backward-char "\e!": complete-command "\e/": complete-filename "\e@": complete-hostname "\e{": complete-into-braces "\e~": complete-username "\e$": complete-variable # copy-backward-word (not bound) # copy-forward-word (not bound) # copy-region-as-kill (not bound) ....

touch /forcefsck

The above command will produce an empty folder ‘forcefsck‘, under root directory. This will force Linux System to examine the file system on the very next boot.

root@...... [~]# touch /forcefsck

Effective Linux Commands that Known Lesser

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