man pages section 2: System Calls
    
U
 
 ulimit — get and set process limits ( Index Term Link )
 
 umask — set and get file creation mask ( Index Term Link )
 
 umount — unmount a file system ( Index Term Link )
 
 umount2 — unmount a file system ( Index Term Link )
 
 uname — get name of current operating system ( Index Term Link )
 
 unlink — remove directory entry ( Index Term Link )
 
 unlinkat — remove directory entry ( Index Term Link )
 
 unmount a file system — umount2 ( Index Term Link )
 
 unmount a file system — umount ( Index Term Link )
 
 user audit identity
  get user audit identity — getauid ( Index Term Link )
  set user audit identity — setauid ( Index Term Link )
 
 user ID, set real and effective — setreuid() ( Index Term Link )
 
 user IDs
  get — getuid, geteuid ( Index Term Link )
  set — setuid ( Index Term Link )
 
 utime — set file access and modification times ( Index Term Link )
 
 utimes — set file access and modification times ( Index Term Link )