在本地某次启动db2时报错SQL1042C，具体报错如下

[db2inst1@standby ~]$ db2start
05/07/2025 16:32:53     0   0   SQL1042C  An unexpected system error occurred.
SQL1032N  No start database manager command was issued.  SQLSTATE=57019

在网上百度到说是需要进行db2iupdt db2inst1来更新实例，于是进行db2iupdt

尝试启动还是报一样错，百度无果，只能查看诊断日志来定位，一开始只看到最后一行，以为是lock 文件的问题，但是删除和修改权限都不行

将日志再往上翻发现了有几个Error信息，里面写道Security-related files do not have required OS permissions，怀疑是某些文件权限不足导致，下面又写道DATA #1 : File name, 37 bytes /home/db/db2inst1/sqllib/adm/fencedid DATA #2 : String, 38 bytes sqllib/adm/fencedid not owned by root. DATA #3 : String, 27 bytes Run db2iupdt command first.
大意是fencedid文件权限不属于root

我们来查看该文件的具体权限，发现其属于db2inst1

将其权限修改为root，启动成功

在之前还遇到过好几次SQL1042C的问题，在此一并总结

1.由于内存或者句柄等限制导致启动失败，其报错信息由于涉密在此不详述，大体关键字为limits等
该问题需要修改 /etc/sysctl.conf
以下为参考

fs.file-max = 6815744
kernel.sem = 10000  10240000 10000 1024
kernel.shmmni = 4096
kernel.shmall = 1073741824
kernel.shmmax = 751619276800
net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default = 16777216
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.core.wmem_default = 16777216
fs.aio-max-nr = 6194304
vm.dirty_ratio=20
vm.dirty_background_ratio=3
vm.dirty_writeback_centisecs=100
vm.dirty_expire_centisecs=500
vm.swappiness=10
vm.min_free_kbytes=524288
net.core.netdev_max_backlog = 30000
net.core.netdev_budget = 600
#vm.nr_hugepages =
net.ipv4.conf.all.rp_filter = 2
net.ipv4.conf.default.rp_filter = 2
net.ipv4.ipfrag_time = 120
net.ipv4.ipfrag_low_thresh = 41943040
net.ipv4.ipfrag_high_thresh = 40894464
net.ipv4.ipfrag_max_dist = 1024
kernel.panic_on_oops=1

sysctl -p生效

2.还有一个是由于数据库的cfg和/etc/hosts不一致，报错是SQL6048N

SQL6048N  A communication error occurred during START or STOP DATABASE MANAGER processing. 
SQL1032N  No start database manager command was issued.  SQLSTATE=57019 

查看db2nodes.cfg和/etc/hosts的主机名不一致

将db2nodes.cfg中的主机名修改为/etc/hosts中的主机名解决