How to view software RAID status on Linux

You can simply view /proc/mdstat:

cat /proc/mdstat

Example output

Personalities : [raid1] [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid10] 
md2 : active raid5 sdb3[4] sdd3[0] sda3[2] sdc3[1]
      2111434752 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
      [===>.................]  recovery = 16.2% (114244316/703811584) finish=48.8min speed=201053K/sec
      bitmap: 2/6 pages [8KB], 65536KB chunk

md1 : active raid1 sdb2[3] sda2[2] sdd2[0] sdc2[1]
      1046528 blocks super 1.2 [4/4] [UUUU]
      
md3 : active raid5 sdb4[4] sda4[2] sdd4[0] sdc4[1]
      44661594624 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
        resync=DELAYED
      bitmap: 2/111 pages [8KB], 65536KB chunk

md0 : active raid1 sda1[2] sdb1[3] sdd1[0] sdc1[1]
      33520640 blocks super 1.2 [4/4] [UUUU]
      
unused devices: <none>