What exactly does a Command Sergeant Major (CSM) do?

In my nearly 30 years, I saw many variations of what a CSM actually did. In the early 70's I saw some who did spend most of their time in the mess hall drinking coffee and spending the day waiting to go to the club. That is not sour grapes since I was a cook, I saw him. Then I saw the hard but fair mean ass SOB like CSM Plumbly as played by Sam Elliott in We Were Soldiers. I was looking for a line item duty description when I attended the Sergeants Major Academy, but there really wasn't one. Yes, senior enlisted advisor to the commander of all matters pertaining to enlisted members of the unit. Also individual training, so that the commanders can focus on collective training. Keeping and teaching Army and unit history, customs and traditions. No CSM has authority on their own, which was greatly misunderstood in my day. Their respective commander must make it clear to the command, especially to the officers, what authority their CSM has within the unit. Then the CSM has got to respect those officers and not act superior, regardless of the stories of CSMs chewing LT and CPT assess. My opinion, but Command Sergeants Major are Sergeants Major OF the Command, not Sergeants Major IN Command. In Combat, the CSM travels the length and width of the commands footprint checking on soldiers, making sure they have what they need to do their jobs and getting what they need to stay physically, mentally, emotionally, and spiritually healthy. Nothing in writing, all natural leadership built in over years.

Advises the commanding officer on all matters pertaining to enlisted personnel.

Also walks around like a ninja correcting unsuspecting privates.

Walk on the grass. You'll find out.

In all seriousness, they advise the commander on all soldier issues and NCO development. In training the commander and CSM work together to train the unit spanning individual to collective levels. The CSM is referred to as the conscience of the command and is the bearer of standards.

In practical terms, they are assigning NCOs to units and positions in conjunction with the 1SGs at Company Level. They supervise the soldier promotion board process. They manage talent. The CSM protects the unit colors. The CSM screens personnel actions and provides advice along with the XO and DCO (at BDE level). The CSM will advise the staff where it is appropriate.

There is magic in the sauce which is not scientific. The biggest piece is variable, it is based on the Commander/CSM individual relationship. My CSM was an extension of my command. I delegated numerous things to her. We talked about most of my key decisions and how they would be implemented before I rolled them out. Sometimes, she was uniquely suited to the function/mission at hand and rolled with it, with my full endorsement. Other times it was me.