When analyzing process states in Linux using ps command, you'll occasionally encounter processes marked with D, Ds or D+. While they all represent uninterruptible sleep states, the additional characters provide important context about the process's behavior and status flags.

The base D state indicates a process in uninterruptible disk sleep, typically waiting for I/O operations to complete. This is the most severe sleep state where the process cannot be killed (even with SIGKILL) until the I/O completes.

ps -eo pid,stat,cmd | grep " D "
 1234 D    /usr/sbin/some_daemon

The additional characters after D reveal important process attributes:

• D+: Process is in uninterruptible sleep AND is in the foreground process group
• Ds: Process is in uninterruptible sleep AND is a session leader

Here's how to identify these states with additional context using a more detailed ps command:

ps -eo pid,stat,uid,cmd,wchan:32 | grep -E " D[+s]?"
12987 D+   1000 du              o2net_send_message_vec
14532 Ds    0   [kworker/1:2]   nvme_wait_cmd

Understanding the differences helps in:

• Troubleshooting hung processes (D+ processes might indicate foreground processes stuck in I/O)
• Identifying critical system processes (Ds often marks important daemons)
• Debugging complex system issues where process groups matter

Combine with other tools for deeper analysis:

strace -p [PID_OF_D_STATE_PROCESS]
# And for kernel-level tracing:
perf trace -p [PID]

Remember that processes in D state for prolonged periods may indicate hardware or filesystem issues that need investigation.

When examining process states in Linux using ps, you'll occasionally encounter processes marked with D, D+, or Ds. These represent different variations of the "uninterruptible sleep" state, which occurs when a process is waiting for an I/O operation to complete.

The single-letter status codes can be augmented with additional characters that provide more context:

D  - Uninterruptible sleep (usually waiting for I/O)
D+ - Process is in uninterruptible sleep and is in the foreground process group
Ds - Process is in uninterruptible sleep and is a session leader

Here's how you might see these states in practice:

$ ps -e -o pid,stat,comm,wchan=WIDE-WCHAN-COLUMN | grep D
  PID STAT COMMAND         WIDE-WCHAN-COLUMN
12987 D+   du              o2net_send_message_vec
14532 Ds   dd              wait_for_buffer
17894 D    kworker/u4:3    nvme_wait_freeze_timeout

Processes stuck in D state can indicate potential issues:

1. Storage device failures or timeouts
2. Network filesystem hangs
3. Driver bugs or hardware issues

For deeper investigation, try these commands:

# Show processes with wait channel information
ps -e -o pid,stat,comm,wchan:32

# Check for D state processes with open files
lsof -p $(ps -e -o pid,stat | awk '$2 ~ /^D/ {print $1}')

# View kernel stack traces for processes in D state
sudo cat /proc/$(ps -e -o pid,stat | awk '$2 ~ /^D/ {print $1}')/stack

The additional markers (+ and s) indicate:

• D+: The process is in the foreground process group of its controlling terminal
• Ds: The process is a session leader (typically the first process in a new session)

When encountering these states:

# Check for disk I/O wait
vmstat 1 5

# Examine disk stats
iostat -x 1 5

# Check system logs for related errors
dmesg | tail -50