When using Paramiko’s Channel.recv()
or exec_command()
with commands producing large outputs, you may encounter BufferError
due to excessive data buffering. This guide shows memory-efficient techniques—streaming, chunked reads, and pagination—to avoid BufferError and handle large SSH outputs robustly.
1. Understand BufferError Causes
- Accumulating entire stdout in memory via
stdout.read()
on large outputs. - Paramiko’s internal buffer hitting capacity limits when data is unread.
- Blocking reads without emptying buffer regularly.
2. Stream Output Line by Line
Process each line as it arrives to avoid buffering the full output:
stdin, stdout, stderr = ssh.exec_command('your_large_command') for line in stdout: process(line) # handle each line immediately
Tip: Use
stdout.readline()
in a loop to control memory usage precisely.3. Read in Fixed-Size Chunks
Read bytes in manageable chunks rather than entire output:
buffer_size = 1024 * 16 # 16 KB stdin, stdout, stderr = ssh.exec_command('your_large_command') while True: chunk = stdout.read(buffer_size) if not chunk: break process(chunk)
This frees each chunk after processing and prevents large buffer buildup.
4. Use Non-Blocking Mode and recv_ready()
Poll the channel for available data and read incrementally:
channel = ssh.get_transport().open_session() channel.exec_command('your_large_command') channel.settimeout(2.0) while not channel.exit_status_ready(): if channel.recv_ready(): data = channel.recv(1024*16) process(data) else: time.sleep(0.1) # Read any remaining data while channel.recv_ready(): process(channel.recv(1024*16))
Note: This avoids blocking on
recv()
and reads data as soon as available.5. Paginate Command Output
Use remote pagination tools (less
, more
) to limit chunk sizes server-side:
# Page through output 1000 lines at a time command = 'your_command | split -l 1000 --numeric-suffixes=1 /tmp/chunk_' ssh.exec_command(command) # Retrieve each chunk file sequentially for i in range(1, 100): filename = f"/tmp/chunk_{i:02d}" stdin, stdout, stderr = ssh.exec_command(f'cat {filename}') for line in stdout: process(line) ssh.exec_command(f'rm {filename}')
6. Clean Up and Close Channels
Always close channels and free resources:
stdout.channel.close() stderr.channel.close() stdin.channel.close() ssh.close()
7. Summary Checklist
- Stream line-by-line rather than reading all at once.
- Read in fixed-size chunks to limit memory use.
- Use non-blocking mode and
recv_ready()
to poll data. - Paginate large outputs server-side to break into smaller files.
- Close channels explicitly to release buffers.