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一般当系统挂掉时没看到下面的log
linux-pnm4:/var/log #
Message from syslogd@linux-pnm4 at Feb 23 09:14:52 ...
kernel:[ 838.942245] Internal error: Oops - BUG: 0 [#1] SMP
这种情况下通过改变log level也无法打印，这个时候可以通过cat /proc/kmsg 这里会实时将dmesg中的log打印到串口上，
这样一般就可以看到出问题的点.
linux-pnm4:~ # cat /proc/kmsg
<47>[ 617.651769] systemd-journald[1463]: Successfully sent stream file descriptor to service manager.
<47>[ 617.671703] systemd-journald[1463]: Successfully sent stream file descriptor to service manager.
<6>[ 627.290487] BTRFS info (device sda1): qgroup scan completed (inconsistency flag cleared)
<47>[ 679.325602] systemd-journald[1463]: Sent WATCHDOG=1 notification.
<4>[ 682.539798] ------------[ cut here ]------------
<2>[ 682.544415] kernel BUG at ../include/linux/skbuff.h:1975!
<4>[ 682.554586] Modules linked in: fuse xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT xt_tcpudp tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables x_tables ib_umad ib_ipoib mlx5_ib rpcrdma sunrpc rdma_ucm nls_utf8 ib_iser isofs rdma_cm iw_cm ib_cm libiscsi scsi_transport_iscsi loop hns_roce_hw_v2 hns_roce ib_uverbs nls_iso8859_1 nls_cp437 vfat fat xfs libcrc32c ib_core ipmi_ssif marvell aes_ce_blk crypto_simd cryptd joydev aes_ce_cipher crc32_ce crct10dif_ce ghash_ce aes_arm64 sha2_ce sha256_arm64 sha1_ce sbsa_gwdt mlx5_core hns3 ixgbe ses enclosure igb mlxfw tls hclge xfrm_algo i2c_algo_bit ipmi_si devlink hnae3 mdio ipmi_devintf ipmi_msghandler