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Check disk space in linux using df command

Linux Version & distribution used for this article
[root@localhost workspace]# uname -sr
Linux 2.6.32-279.el6.x86_64

[root@localhost workspace]# cat /etc/redhat-release

CentOS release 6.3 (Final)

1. df -- It display available file system details like device name, total size, used space and available space

[root@localhost workspace]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
18133780 3579124 14370472 20% /
tmpfs 247288 420 246868 1% /dev/shm
/dev/sda1 495844 33920 436324 8% /boot

2. a -- include dummy filesystem

[root@localhost workspace]# df -a
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
18133780 3591168 14358428 21% /
proc 0 0 0 - /proc
sysfs 0 0 0 - /sys
devpts 0 0 0 - /dev/pts
tmpfs 247288 420 246868 1% /dev/shm
/dev/sda1 495844 33920 436324 8% /boot
none 0 0 0 - /proc/sys/fs/binfmt_misc
vmware-vmblock 0 0 0 - /var/run/vmblock-fuse
sunrpc 0 0 0 - /var/lib/nfs/rpc_pipefs

3. h -- human readable format. It will display size format as GB, MB, KB

[root@localhost workspace]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_fedo-lv_root
18G 3.5G 14G 21% /
tmpfs 242M 420K 242M 1% /dev/shm
/dev/sda1 485M 34M 427M 8% /boot

4. df -h / -- Display only certain mount point

[root@localhost workspace]# df -h /
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_fedo-lv_root
18G 3.7G 14G 22% /

[root@localhost workspace]# df -h /boot
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 485M 34M 427M 8% /boot

5. df -B 512 -- we can change the size of block its displaying. Below example each block has 512 bytes

[root@localhost workspace]# df -B 512
Filesystem 512B-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
36267560 7636832 28262360 22% /
tmpfs 494576 864 493712 1% /dev/shm
/dev/sda1 991688 67840 872648 8% /boot

6. df --block-size=512k -- display block in KB format. here it will show each block is 512kb

[root@localhost workspace]# df --block-size=512k
Filesystem 512K-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
35418 7458 27600 22% /
tmpfs 483 1 483 1% /dev/shm
/dev/sda1 969 67 853 8% /boot

7. m -- display block size in MB

[root@localhost workspace]# df -m
Filesystem 1M-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
17709 3729 13800 22% /
tmpfs 242 1 242 1% /dev/shm
/dev/sda1 485 34 427 8% /boot

8. --total -- display the grand total

[root@localhost workspace]# df --total
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
18133780 3818416 14131180 22% /
tmpfs 247288 432 246856 1% /dev/shm
/dev/sda1 495844 33920 436324 8% /boot
total 18876912 3852768 14814360 21%

9. i -- list inode information instead of block usage

[root@localhost workspace]# df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/mapper/vg_fedo-lv_root
1155072 138135 1016937 12% /
tmpfs 61822 7 61815 1% /dev/shm
/dev/sda1 128016 40 127976 1% /boot

10. T -- It will display additionaly filesystem type like ext3, ext4.

[root@localhost workspace]# df -T
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
ext4 18133780 3818420 14131176 22% /
tmpfs tmpfs 247288 432 246856 1% /dev/shm
/dev/sda1 ext4 495844 33920 436324 8% /boot

11. t -- helps to display specific type of file system

[root@localhost workspace]# df -Tt ext4
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_fedo-lv_root
ext4 18133780 3818412 14131184 22% /
/dev/sda1 ext4 495844 33920 436324 8% /boot

12. x -- exclude specific type of file system

[root@localhost workspace]# df -Tx ext4
Filesystem Type 1K-blocks Used Available Use% Mounted on
tmpfs tmpfs 247288 432 246856 1% /dev/shm

13. df --help -- to get df command help information

ENJOY & HAVE FUN WITH LINUX!!!!

Vector and Iterator in C++

PROGRAM:

#include <iostream>
#include <vector>

using namespace std;

int main(int argc, char *argv[])
{
        vector<int> myarr;

        cout << "\nSize : " << myarr.size() << endl;

        //put data at vector
        myarr.push_back(5);
        myarr.push_back(10);
        myarr.push_back(15);
        myarr.push_back(20);
        myarr.push_back(25);

        cout << "\nSize : " << myarr.size() << endl;
        for (int i = 0; i < myarr.size(); i++)
                cout << "\tArray values " << myarr[i] << endl;

        //delete first value
        myarr.erase(myarr.begin());

        cout << "\nSize : " << myarr.size() << endl;
        for (int i = 0; i < myarr.size(); i++)
                cout << "\tArray values " << myarr[i] << endl;

        //delete last value
        myarr.erase(myarr.end()-1);

        cout << "\nSize : " << myarr.size() << endl;
        for (int i = 0; i < myarr.size(); i++)
                cout << "\tArray values " << myarr[i] << endl;

        //insert at position
        myarr.insert(myarr.begin()+2, 100);

        cout << "\nSize : " << myarr.size() << endl;
        for (int i = 0; i < myarr.size(); i++)
                cout << "\tArray values " << myarr[i] << endl;

        //delete middle value
        myarr.erase(myarr.begin()+1);

        cout << "\nSize : " << myarr.size() << endl;
        for (int i = 0; i < myarr.size(); i++)
                cout << "\tArray values " << myarr[i] << endl;

        return 0;
}

OUTPUT:

Size : 0

Size : 5
        Array values 5
        Array values 10
        Array values 15
        Array values 20
        Array values 25

Size : 4
        Array values 10
        Array values 15
        Array values 20
        Array values 25

Size : 3
        Array values 10
        Array values 15
        Array values 20

Size : 4
        Array values 10
        Array values 15
        Array values 100
        Array values 20

Size : 3
        Array values 10
        Array values 100
        Array values 20

Introduction to GNU profiler

Introduction:

Profiling is the process of finding the time complexity of program.

Profiler will find the time taken by the parts of the code. It will help to programmer
to reconstruct the code if the parts of the code consumed more time.

There is many profiling tools available. But this article give idea on native GNU profiler(gprof)

Step 1:

Write a simple program called proftest.c

#include <stdio.h>
void firstFunction(int );
void secondFunction(int );

int main(int argc, char *argv[])
{
int a = 10;
int *b = &a;
firstFunction(a);
return 0;
}

void firstFunction(int a)
{
a += 10;
sleep(1);
secondFunction(a);
return;
}

void secondFunction(int b)
{
sleep(5);
printf("final value : %d\n", b);
return;
}

step 2:
Compile the program with '-pg' option using gcc

gcc -pg proftest.c -o profout

Step 3:
Execute the program

./profout

It will create the gmon.out file in current directory

step 4:
run the gprof with gmon.out

gprof -b profout gmon.out

You will get the output as below

Flat profile:

Each sample counts as 0.01 seconds.
no time accumulated

% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 1 0.00 0.00 firstFunction
0.00 0.00 0.00 1 0.00 0.00 secondFunction

Call graph

granularity: each sample hit covers 2 byte(s) no time propagated

index % time self children called name
0.00 0.00 1/1 main [7]
[1] 0.0 0.00 0.00 1 firstFunction [1]
0.00 0.00 1/1 secondFunction [2]
-----------------------------------------------
0.00 0.00 1/1 firstFunction [1]
[2] 0.0 0.00 0.00 1 secondFunction [2]
-----------------------------------------------

Index by function name

[1] firstFunction [2] secondFunction

C Program To Reverse Singly Linked List

PROGRAM:

#include <stdio.h>
#include <stdlib.h>

typedef struct _list {
int data;
struct _list *next;
}list;

int main(int argc, char **argv)
{
printf("\n.. Start of singly linked list reverse program .. \n\n");

list *head=NULL, *head_start=NULL, *display = NULL;
list *newnode;
int a = 0;

/* Add 5 elements to linked list */
for (; a<10; a++)
{
newnode = malloc(sizeof(list));
newnode->data = a+1;
newnode->next = NULL;
if (a==0) {
head = newnode;
head_start = newnode;
}
else {
head->next = newnode;
head = head->next;
}
}

C program to check file available in a path

PROGRAM:

#include <stdio.h>
#include <unistd.h>
 
int main(void) {
    if( access("/home/pc/test.txt", F_OK) != 0 )
                printf("File not available\n");
        else
                printf("File available\n");
        return 0;
}

OUTPUT:
File not available