To take backup of all databases in mongodb

List all databases;

show dbs;
admin 0.000GB
local 0.000GB
twitter 0.720GB
viva 0.061GB

1. DUMP ALL THE DATABASES IN MongoDB
Default dump location is :  /dump

SYNTAX : 

mongodump -h <hostname>

sachin@sachin-Inspiron-15-3567:~/dump$ mongodump -h localhost 
2017-12-03T00:04:44.665+0530 writing admin.system.version to 
2017-12-03T00:04:44.667+0530 done dumping admin.system.version (1 document)
2017-12-03T00:04:44.668+0530 writing twitter.kashmir to 
2017-12-03T00:04:44.668+0530 writing twitter.total to 
2017-12-03T00:04:44.668+0530 writing twitter.repo to 
2017-12-03T00:04:44.668+0530 writing twitter.northkorea to 
2017-12-03T00:04:44.832+0530 done dumping twitter.total (35927 documents)
2017-12-03T00:04:44.832+0530 writing twitter.twitte2 to 
2017-12-03T00:04:46.020+0530 done dumping twitter.repo (35927 documents)
2017-12-03T00:04:46.020+0530 writing viva.external to 
2017-12-03T00:04:47.006+0530 done dumping twitter.twitte2 (35922 documents)
2017-12-03T00:04:47.006+0530 writing twitter.sahpur to 
2017-12-03T00:04:47.645+0530 [######..................] twitter.kashmir 54868/210000 (26.1%)
2017-12-03T00:04:47.645+0530 [#########...............] twitter.northkorea 46152/116954 (39.5%)
2017-12-03T00:04:47.645+0530 [#########...............] viva.external 14022/35922 (39.0%)
2017-12-03T00:04:47.645+0530 [##......................] twitter.sahpur 3133/26000 (12.0%)
2017-12-03T00:04:47.645+0530 
2017-12-03T00:04:50.645+0530 [#######.................] twitter.kashmir 69317/210000 (33.0%)
2017-12-03T00:04:50.645+0530 [###########.............] twitter.northkorea 56084/116954 (48.0%)
2017-12-03T00:04:50.645+0530 [################........] viva.external 25361/35922 (70.6%)
2017-12-03T00:04:50.645+0530 [###########.............] twitter.sahpur 12334/26000 (47.4%)
2017-12-03T00:04:50.645+0530 
2017-12-03T00:04:52.317+0530 [########################] viva.external 35922/35922 (100.0%)
2017-12-03T00:04:52.317+0530 done dumping viva.external (35922 documents)

Check Dump Location

sachin@sachin-Inspiron-15-3567:~$ ls
Desktop Downloads examples.desktop Music Pictures Templates Videos
Documents dump mongodb-compass_1.6.0_amd64.deb pgadmin.log Public tweepy VirtualBox VMs

sachin@sachin-Inspiron-15-3567:~$ cd dump/

sachin@sachin-Inspiron-15-3567:~/dump$ ls
admin twitter viva

All databases dump created with folder name

2. If you want to dump specific database

mongodump --db database_name

3. If you want to dump only one collection in database

mongodump --db database_name --collection cdac

4. If you want to dump all but cdac collection

 mongodump --db database_name --excludeCollection=users

5. It is also possible to output the dump to an archive file:

mongodump --archive=test.archive --db database_name

6. Backup database having password

mongodump --username sachin --password xyz@123 --authenticationDatabase admin