I generated a bam file following the below steps:

indexed reference genome

bwa index reference.fasta

aligned using bwa mem

bwa mem  ref.fasta f1.fq.gz f2.fq.gz > out.sam

sam to bam

samtools view  -Sb out.sam > out.bam

sorting bam

samtools sort out.bam sorted

Now, I am looking at bam file:

samtools view sorted.bam | less

output

ST-E00318:201:HWN2CCCXX:6:1104:25134:16867      163     NC_026145.1     1       39      15S59M18D76M    =       221     370     CGCCTGTACGAAGAGATCTTTTTCTTCTCCTACTCGCGCCGTTGCCGCCACTCGTCGTGCCATTCCGCCGCCGTCGGACCACCACCACCCGACTCGCGCTGGGATGACGAAGCCGACCATCCGGTCAGATCATGGATCCGTTCAGTCGCC  AAFFFJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJFJJJJJJJJJJJJJJJJFFJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJJA7JFFFJJJJ  NM:i:19 AS:i:106        XS:i:116
ST-E00318:201:HWN2CCCXX:6:1111:17787:9660       99      NC_026145.1     1       21      6S144M  =       409     558     GAAGAGATCTTTTTCTTCTCCTACTCGCGCCGTTGCCGCCACTCGTCGTGCCATTCCGCCGCCGTCCGGCCACCGTTCGCCGGCGGACCACCACCACCCGACTCGCGCTGGGATGACGAAGCCGACCATCCGGTCAGATCATGGATCCGT  AAAFFJJFJJJJJJJJJJJJJJJJJJJJJJJJJFJJJJJJJJJJJJJJJJJJFJJJJJJJJJJJJJJJFJJFJJJJJJFJJJJJJJAJJAJJJJJAFJJJJJFJJJJJJJJJ7JJJJJJJJJJJFJJJJJJJJJJJJFJJJJJJJFFJJ<  NM:i:2  AS:i:134        XS:i:140

Problem 1: Where are the headers? i.e. @HD and @SQ sections!!

Now, if I do:

samtools view -H sorted.bam | less

Headers [@SQ] are there, isnt that strange!!

@SQ     SN:NC_026145.1  LN:18577331
@SQ     SN:NC_026146.1  LN:18500646
@SQ     SN:NC_026147.1  LN:24928530
@SQ     SN:NC_026148.1  LN:17356267
@SQ     SN:NC_026149.1  LN:18898134
@SQ     SN:NC_026150.1  LN:25289714
@SQ     SN:NC_026151.1  LN:11725536
@SQ     SN:NC_026152.1  LN:21523998
@SQ     SN:NC_026153.1  LN:12411895

Problem 2: Where is the @HD section where I can see the SO (sorting status)?

My samtools version:

Program: samtools (Tools for alignments in the SAM format) Version: 0.1.18 (r982:295)

My BWA version:

Program: bwa (alignment via Burrows-Wheeler transformation) Version: 0.7.5a-r405

Did anybody go through the same problem? Did I miss something?