sudo与stdbuf位置差异及Shell重定向作用范围技术咨询

问题背景 #

运行以下命令时发现部分日志丢失：

root@janux-spr1:/home/tw12/redis_research/dpdk-framework/dpdk-rx# { sudo ./dpdk-rx -l 3-5 -a 0000:18:00.1 -- -m 0 -d 0 -l 1 -i 500; } &> test.log; cat test.log

输出结果：

EAL: Detected CPU lcores: 32
EAL: Detected NUMA nodes: 1
EAL: Detected shared linkage of DPDK
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'PA'
EAL: VFIO support initialized
EAL: Probe PCI driver: mlx5_pci (15b3:101b) device: 0000:18:00.1 (socket 0)
mlx5_common: DevX read access NIC register=0X9055 failed errno=121 status=0x3 syndrome=0x54e3a9
TELEMETRY: No legacy callbacks, legacy socket not created
Floating point exception

推测是缓冲问题，添加stdbuf -o0关闭stdout缓冲后，发现stdbuf的位置会影响结果，只有第二种写法能输出完整日志：

第一种写法（日志仍不完整） #

root@janux-spr1:/home/tw12/redis_research/dpdk-framework/dpdk-rx# { stdbuf -o0 sudo ./dpdk-rx -l 3-5 -a 0000:18:00.1 -- -m 0 -d 0 -l 1 -i 500; } &> test.log; cat test.log

输出：

EAL: Detected CPU lcores: 32
EAL: Detected NUMA nodes: 1
EAL: Detected shared linkage of DPDK
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'PA'
EAL: VFIO support initialized
EAL: Probe PCI driver: mlx5_pci (15b3:101b) device: 0000:18:00.1 (socket 0)
mlx5_common: DevX read access NIC register=0X9055 failed errno=121 status=0x3 syndrome=0x54e3a9
TELEMETRY: No legacy callbacks, legacy socket not created
Floating point exception

第二种写法（日志完整） #

root@janux-spr1:/home/tw12/redis_research/dpdk-framework/dpdk-rx# { sudo stdbuf -o0 ./dpdk-rx -l 3-5 -a 0000:18:00.1 -- -m 0 -d 0 -l 1 -i 500; } &> test.log; cat test.log

输出：

EAL: Detected CPU lcores: 32
EAL: Detected NUMA nodes: 1
EAL: Detected shared linkage of DPDK
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'PA'
EAL: VFIO support initialized
EAL: Probe PCI driver: mlx5_pci (15b3:101b) device: 0000:18:00.1 (socket 0)
mlx5_common: DevX read access NIC register=0X9055 failed errno=121 status=0x3 syndrome=0x54e3a9
TELEMETRY: No legacy callbacks, legacy socket not created
5 EAL arguments used
0 application arguments used
================ Configuration ================
Port:           0
Interval:       500 msec
Packet Rate:    N/A (no rate limiting)
===============================================
RX lcore count: 3
Allocated mbuf pool size 71303168B
Init port 0
PCI address: 0000:18:00.1
Set up 2 TX rings (4096 descriptors per ring)
Set up 2 RX rings (4096 descriptors per ring)
Port 0 MAC: b8 3f d2 59 5f e1
CPU running in 2000 MHz, printing interval is 500ms -- 1000000000 cycles
Starting RX Threads -- Main thread NOT treats as RX thread
lcore  4 (lcore index  1, RX index  0) starts to receive packets
lcore  5 (lcore index  2, RX index  1) starts to receive packets
Floating point exception

通用问题 #

1. 重定向的作用范围是什么？重定向和缓冲设置仅作用于所附加的特定命令吗？如果是，那么对于包含多个子命令的组合（如sudo time XXX或bash -c ''）情况如何？
2. 对于sudo time XXX > logfile，重定向的是XXX还是整个sudo time XXX？类似的，command1 && command2 > logfile && command3、{command1 && command2} > logfile等场景的重定向规则是什么？

命令解析学习资源 #

已查阅过单词拆分相关资料，但仍不清楚Bash如何判断某个词是独立命令还是前一个命令的参数，哪里可以系统学习这些知识？

内容的提问来源于stack exchange，提问作者user12815541